Last year I barely used the trainer, maybe a handful of times the entire year ... results were not so good...
This year, I have used the spin-bike (during early winter months) and the regular fluid trainer in early pre-season and the results have been considerably better.
I can't say that the results are entirely due to using the trainers, but a combination of lower body-weight and increased power due to more controllable environments allowed by the trainer and power meter display unit.
I have improved a lot by incorporating them so far, at this point I don't see any reason to completely stop using it.