My last road bike was a 2006 Specialized with all 105 (10-speed). After riding it for a year, I sold it to a friend and bought a 2005 Terry that is all Ultegra (9-speed). I swore I'd never go back. The Ultegra is significantly nicer in my book. It's smoother shifting and it stays tuned. I was constantly having to adjust (and have adjusted) my 105 bike but this one still shifts like silk 2 years later! I'm pretty hard on my stuff, and the Ultegra is holding up very, very well.

I don't know if there is a something about the 9-speed and the 10-speed groups that might be part of the difference, but in my limited experience, Ultegra was well worth the upgrade.

I'm thinking of building up my next bike and I'd like to do it with 9-speed Ultegra again if I can. It works for me, so I want to stick with it. That said, I agree that there is no point in going into debt to upgrade. There are many, many people out there who are perfectly happy with 105 components! In fact, until I got my Ultegra bike - I didn't know any better and was happy with the 105. (Now I've been spoiled which is why I hope to never ride Dura Ace ).