I switched to 3.0 when it came out - I didn't really have much choice at the time, if I wanted to continue on as a freelance writer for Dragon and Dungeon magazines - but immediately came to love it. So much had been changed for the better, rules-wise, and the possibilities were so wide open as far as character creation. I felt a little constricted at first in the monster selection, because unlike during the 1E to 2E switch you couldn't really just take the monster stats from the previous edition and run with them, they needed a much bigger conversion effort, but over time (and subsequent monsters in the Fiend Folio, Monster Manual X books, and even third-party works like the indispensable Tome of Horrors) things got better on that front. (And, I have to admit, the 3E Monster Manual did do a good job of providing a decent initial selection of monsters.)
When 4E came out and I had to make the same choice again - purchase and learn the new edition or leave my freelancer days behind me - I stuck with 3.5 and never looked back. (I'm not slamming 4E, it just didn't look like the changes they'd made to the game were going to be my cup of tea, nor those of my players.) I've been playing 3.0/3.5 since the edition(s) first came out and I don't see myself ever needing to move on from it. Sure, higher level combat starts to get clunky at times but I've found I don't mind the extra effort and I've been blessed with players who build characters they think will be fun to play, not seek the most broken loophole combinations they can come up with.
It's been a good 20 years and I look forward to the next 20 years of 3.5 gaming.
Johnathan