Hello.
My name is stve and i am a GM.
I wont be using 3.5e in my game.
Why?
My game has run for 11 levels now, from 2nd to 13th, and you know by now all those niggling 3.0 issues like haste too good and hour long buffs and such have either been addressed or handled. Its not wrong for a sor with extend to be able to buff for 24 hours, its just one of the things being 12th level means.
I considered moving to 3.5 but the downside of that is too much of what has gone before" and the decisions in character design suddenly overnight become wrong choices and tactics learned become errors that need to be rethought.
All in all, the impact on 3.0 characters at mid levels is severe even if i could get them all to forget all the events that went before and start trying to figure out tactics for a radically different game, their spell choices and magic items choices are now in many cases bad choices.
The transition would not be a smooth one. I think WOTC may have started with the notion of it being a smooth transition but lost that along the way.
Also, after hearing from people who apparently have books in hand, i now realize that in addition to some few big changes, there are a lot, a whooe lot, of little changes. bobbi shouldn't need to relearn her barbarian and sandy should not need to redo his sorcerer when our game has been running without breaking and with everyone enjoying it for 11 levels.
When i run my next fantasy game, i will reconsider 3.5, but frankly, both midnight and arcana unearthed sound more interesting for fantasy worlds.
So, my advice to a player who has a Gm insisting on change would be to take him aside and discuss it from the point of view of treating it like a software upgrade. has the current game been unfun or broken in play or have people been having fun? if the answer is it has been playing fine then the need for a radical transition to the new version seems to be lacking. Upgrading for the sake of upgrading in midrun is usually bad.
if he has his heart set on it, then your options are adapt or quit and run your own game.