I play in one game that will almost assuredly continue in 3.5. Since the core rules won't include the equivalents of the Druid, Monk and Bard, we would have 60% of the group that would have difficulties converting. The fact that even third parties won't be able to address that gap until October really clinches the fact that we won't convert.
I run a game where if we were to choose to move from 3.5, we would be just as likely to migrate to Savage Worlds, or something else, as we are to migrate to 4. But we are enjoying our Ptolus fun. If anything, we are likely to investigate the BoXM series to see if we can bring in some 4e like elements of play. We haven't really decided yet though.
I am getting ready to restart a monthly game for my wife and as many players as we can get that will probably use a mix of 3.0 and 3.5. Again, these are established characters and we are restarting the campaign for the character development. From what I can see, it would be challenging to convert her 3.0 telepathic Psion/Ghostbreaker into 4e.
For my son, I will continue with BFRPG for a little bit, then I will introduce him to a completely different set of mechanics. We will play that for a little while, then shift again. We will do that until we have gone through all sorts of games and mechanics. I want him to have a broad range of experience so he can appreciate all the flexibility of gaming and will be comfortable playing anything until he settles into his own favorite systems.
I am sure I will play 4e at some point. I'm just not in a rush at this point. WotC's development plan this time around makes it challenging to convert existing games and all of the games I am running/playing have not reached the point of conclusion.