I think you have to combine it with reading articles and watching videos. When you do it like that I think the tactics stick better in your brain.
Also sometimes when I use the TT I decide to not go for quick resolving, but for 100% certainty solving. So I take as long as I need to solve the tactic and dont worry about time. When I do that I also have to check WHY the tactic works. Is there no save? All the way untill I completely understand what is going on.
The feeling of spinning your wheels.
This is my standing on the matter as of me writing this:
Your Rating: 1189
Today's Attempts: 59 (Average Score: 45%)
At some point today I was within a good score of getting back over 1300 (had made it to 1290 range).
I've never been over 1450 and I've been a premium member for nearly a year. Tactics Trainer is the tool I use most and I have to be doing it wrong because it's claim of sharpening my tactical vision isn't helping me.
Man, some of these exercises leave me cursing under my breath as I miss something plainly easy and my score drops yet again.