does the tactics trainer on chess.com actually help?

YES

You can memorize all the tactics you want, but if you dont know how to get to those positions it wont help.  Just like openings.  If all youre doing is memorizing opening moves, and not understanding "why" you make those moves, your game will not improve.  

I think there are certain mate shapes you should know: kh8, Nf6 and Rg8 or Rh7 being one.

A combination: kg8, qa5, nf6, bg7 ; Qd2, Nc3, Bg5 where the theme is BxN BxB ; Nd5 --- Now if the Qd2 is protected by a rook and black cannot play Qd8 then a piece is lost by black.

Another at risk shape is Bf4, Nf3, Bd3 if black can advance a supported pawn to e5 and e4.

I can't speak for advanced players, but for people who start at the bottom (I'm one of those) I know it has already worked. I now stop playing  for a few days and am back for more tactic training (more advanced and really convoluted (how can you see,as a beginner, that you have a potential check mate when you've not seen those before). And I see that the GM and great players all work on tactics. I tend to think that chess is like music, that you have to practice your scales every day. And anyway, tactic training is really cool after a couple of beers and should be part of the chess daily diet (the tactic training, not the beer).

my tactics rating is very low, but I'm still in about the top 90% in any game over 5 minutes....guess I know something else??? endgame/strategy/timing??? I don't know for sure, but I think if you just know that a queen and a bishop is much better than a rook and a pawn you can make something happen....just may not be elegant...like killing ants with a sledge hammer to me

Agreed. I brought this up in another forum about tactics. How much of it is learning vs just memorizing? If the point of tactics is to memorize an exact position in a random game and the moves to gain an advantage, then that's not very helpful at all. But I do think tactics do more than that. Especially in the beginning, tactics taught me how to think, and find them in my games even if I hadn't seen them before. I see it more as a set of tools than a map.

Smother mates show up a lot in tactics. And yes, they can obviously help you if you get into that exact position. But they can also teach you how to think about space and movement, and what a lack of both do to your opponent.

Im not big on studying tactics, so i need to "short cut" things.  I look for 2 things:

1. Piece interaction.

2. Forcing Moves.

@urk I disagree with you that tactics is not important. Specifically for players below 2000 it is very important, since many games decided by tactics. Purpose of tactics is to get familiar with all the patterns and themes, It is prerequisite to learn tactics to reach passed a certain rating. I am not saying they should spend a lot of time in that, even half an hour daily( or once in few days) is enough to stay sharp. Of course other things are also very important.

I understand that the idea behind doing a set of simple tactics repeatedly until you know them cold is so that you recognise the pattern when you do more difficult positions. 2Q1C's post 7 is a good example - if you're looking at a position and see that pattern arising a few moves ahead in a variation you think "that's it - White now mates". You'd probably still need to check it to checkmate in case there's some detail that stops it working, but you would at least know the variation was worth analysing.

I think it's pretty useful for building up pattern recognition, but I agree if that's all someone was doing for training, law of diminishing returns would kick in pretty quickly.

My  training plan at the moment is: 

• Online Game 45|45 (played OTB) or Club game.
• Self Analysis of above game, (looking for blunders unassisted).
• Computer assisted analysis of above game.
• Opening theory. (discovering chess openings, John Emms. Then more opening specific books). 
• Tactical theory. (predator at the chessboard, Ward Farnsworth, Vol 1&2). 
• Endgame Theory, (Complete endgame course, Silman).
• Annotated master games. (Logical chess move by move, Chernev to begin with.)
• Opening Drills, ( training learnt opening ideas using the software Chess Position Trainer.)
• Tactical Drills, (using chess tempo and setting the position on the board).
• Endgame Drills. (Practising learnt endgame positions against an engine.)
• Visualisation Drills, (using the software Chess eye.)

I plan to use a real chessboard for all of the training. 

I may supplement this with daily tactics training-30- 60 mins on CT-Art Beginner tactics  just using the computer screen.

This program is working well for OTB

Tactics are essential to chess growth.  

Get a tactics book.

Study with a real board and pieces.

Online study is ok, but you get much more out of studying on a real set.