I think the TT is a great tool that can be used well both with and without the rating (timer). For pure analysis, I agree it is better without the timer, but for encouraging you to think quickly in a timed framework (like Live or OTB), the timer is very beneficial.
Tactics Trainer

I think you should keep the TT on.
The idea is not to give you time to think, if you want time to think, then you first need to develop it at unrated and/or chesstempo. However, you can do the same, by carefully reviewing the solution when you get it WRONG on Tactics Trainer.
The idea is, you see a mate in 6, and it takes you too long and you get it wrong. That same pattern, will appear again in some time, and then now, it may take you a little less time, and you still get it wrong. Then the next time, you remember the solution and you get it right.
That's the point. You have to do thousands of these problems. It's called pattern development. Of course, most of the time you'll be going down in rating, but don't assume it's not helping you.
But definitely do some unrated for some time too, it might help as well.

No, the timer is stupid. OTB I do not have to calculate a mate in 4 in less then a minute. Most people can't even calculate that deep with 100% accuracy, there is always some little flaw, some zwischenzug a couple plys deep that you can easily miss in many similar positions. There are so many positions in TT where the majority of players that manage to solve the position in TT never would have gone for the variation in a real game because they wouldn't be able to calculate it accurately and esp not as fast as TT wants you to calculate it.
Obviously TT right now is only adjusted for people that want to mainly improve their blitz tactical vision and not general accurate calculation for long timed OTB games. There should be two modes. One like TT now and the other like this:
You can take several minutes and you only get points for winning material or mating. Get more points for mate and more material then winning a pawn.
If you make a bad move you lose points.
This way you could really try to improve for your OTB play where you can't lash out in every position for a some 10 move tactic.
I'm beginning to think I need to master the TT before I will get full benefit out of the CM. I like the setting where the TT stops after each problem. I believe the more thought put into the TT and the CM, the more I learn.
The timer is important, although sometimes aggrevating. I think the idea is to play against the timer but refuse to guess, only move when you have calculated.
Dan Heisman who writes Novice Nook talks about how you need to be able to solve a lot of the basic tactical patterns pretty much by recognition. If you can't recognize the patterns almost instantaneously than you have to solve them rather than reduce to them. For example a four move mating combination involving bishop and queen that comes about as a result of a three move combination involving say a rook sacrifice is the type of problem that is very hard to solve if you don't almost instantly recognize that four move combination.

The timer is important, although sometimes aggrevating. I think the idea is to play against the timer but refuse to guess, only move when you have calculated.
Dan Heisman who writes Novice Nook talks about how you need to be able to solve a lot of the basic tactical patterns pretty much by recognition. If you can't recognize the patterns almost instantaneously than you have to solve them rather than reduce to them. For example a four move mating combination involving bishop and queen that comes about as a result of a three move combination involving say a rook sacrifice is the type of problem that is very hard to solve if you don't almost instantly recognize that four move combination.
Alot of problems higher up are 4-8 move combinations. to accurately calculate against the clock on those is impossible unless you're Alekhine. This is because the timer is based on how fast people solve the problem and 95% of the problems are solved by feeling and not actual 100% calculation which drives the timer down alot.

I think Tactics Trainers is more or less balanced. Sometimes it offers 1 or 2-move problems that should be solved instantly, sometimes up to 1200 seconds (if I remember correctly). The only feature that IS very irritating is that it often forces one to keep playing even in ABSOLUTELY won positions. I.e. White is a queen up, there are no threats, and it makes one search for the shortest way to mate. I'm irritated when it says "wrong" after I mate in 4 instead of 3, etc.
One stupid feature of tactics trainer is the bar that allows you to see your time running out. How is that supposed to help your chess?

One stupid feature of tactics trainer is the bar that allows you to see your time running out. How is that supposed to help your chess?
The bar is really bad because it tells you if you are supposed to look for a 1 move combo that is obvious or if you need to look deeper.
I think a good addition to the TT would be a set of problems where there aren't any tactics but it looks like their might be potential for some and any attempts to force them get marked wrong and normal developing moves get marked correctly. Punish the ratings of people who say "Well there has to be a tactic here so obviously it starts with this".

TT is only one aspect of training, but I am completely converted to its value in the middle game. After 5,572 tries, I never miss a mate in 1, rarely miss a mate in 2, and have a much better eye for mates in three, smothered mates, and beyond. The timer really pushes you to commit yourself, which you often have to do in an OTB game, and I find it so aggravating to be right "the second time" (30% of my TT positions) that I have really pushed myself to look for alternatives with every move.
I think that my middle game is probably my best strength (It's where I win most of my games) and it's due in part to recognising the patterns in TT. Now I just have to work on understanding my openings, my position play, my end games.. ..
Because as you get better in chess, tactics are less likely to trip up your opponent. OTOH, if you don't understand tactics, you are going to be checkmated over and over in the middle of the game.

we have heard you. we will do an untimed, rated version at some point. i don't agree with the reasons (they seem more emotional than logical), but i understand that it is disheartening sometimes to feel pressure. we should also hide the timer by default :)
I feel the system used on www.chesstempo.com is much better. There is both a standard rating and a blitz rating. I would like to see a standard rating used here on this site. I have stopped using the timer as well.
I recently decided to stop using the timer on tactics trainer because it causes me to rush my decision making. I think as an improving player it is more important to do the analysis and try to find the correct answer than to play by gut feeling quickly and hope to get lucky. This is similar to most experts advice to play slow games instead of blitz when trying to improve. I especially dislike how you can take your time and get a mate in 7 problem correct but lose points because you took too long. My other gripe is that if you don't play your puzzles timed then tactics trainer does not keep up with your success rate. I'd like to hear from others about their thoughts on "tactics trainer".