[MENTION=54846]Rechan[/MENTION] I agree with you that the players will want to do something other than character generation at Session Zero. That's why we played a one-shot game with pre-existing characters, wrapping up the careers of their previous characters.
I suppose another option would have been to have pre-gens for the new campaign setting available, but first of all I didn't want to have to create a bunch of new characters beforehand, and second, I didn't want the players to have to learn the pre-gens and THEN learn their own new characters.
We actually did have three laptops at the table, and they were passed around a little bit so that people could use the Character Builder, but I had no interest in everyone taking time to sort through all of the feats and powers for all six characters. We left that for between Session Zero and Session One, and I think that's the right choice.
Like [MENTION=6667124]ffy[/MENTION], I allow total freedom in tweaks and retraining for the first few sessions with new characters. If someone plays a session as a Bard and says "Yuck, I think I'd much rather be something else now that I've seen this in action," I'm fine with that.