I am not sure if this has been done before, but even if so maybe it's worth repeating.

What cycling-related product did you initially think was a really BAD idea but upon further reflection (or just trying it) did you think after all, it's a really GOOD idea/product??

My nominee: Podium Water Bottle (by Camelback). I initially figured, what's wrong with good old fashioned water bottles?? But I finally relented and got one a few months ago and I really like the no-leak valve. The bottle itself is just a bottle but the valve is really a good idea and works amazingly well. No more wearing my drink!

Runner-up: Shimano Di-2 - not that I have tried it yet, but from my reading it sounds like a pretty good product (although maybe it's just a solution in search of a problem).

Second runner up - This thread.

Feel free to add your own Bad Idea/Good Idea nominee.