Great thread!

I just started commuting with any seriousness in 2010, so my list would be long but useless (I don't have much basis for comparison).

Likes:

Topeak Road MorphG. Liked it well enough to buy another to replace it when bike #1 was stolen.
Disk Brakes. I don't know that I'd intentionally buy a bike without them at this point. Perhaps if I rode a new bike with non-disk brakes, I'd be less impressed with disks.
Clipless pedals. I'm a fan. Way easier than toe cages, and I like being locked in. I know others disagree. Thinking about trying some with larger platforms next time around, for those times when I don't want to change shoes for a short ride.
Leaving my main lock on the bike rack at work. Sure, I still carry a lock, but my primary security Kryptonite stays in place, so I don't have to lug it back and forth.
Panniers. Not 100% converted -- if I metro part way, I'll still fall back to the backpack, I think. But for limited walking, I'll put up with the off bike inconvenience, because the on bike utility is great. I'm using Avenir Excursion Lrg, which are fine, but certainly not Ortlieb or other quality. So far, so good, but if I get three years from them, I'll be thrilled. Still haven't had to test their water resistance, either.
My LBS. Customer service is so important!
Bike Forums. My go to source for information and opinions.


dislikes:

cheap lights. Not worth even the small price of entry, generally.
bike thieves. 'nough said.
flat bars. Give me more hand positions!

Positive use, but not enough to "like"

Origin 8 drop bar ends. better than the flat bars, but not a real substitute for drops (or other alternatives that I've not tried).