It just depends on what storylines you take.
So a lot of characters return, but there's still plenty of characters who don't despite being able to, and it's all to easy to pick the "wrong" path so that you're not re-united with old chums... and often, those old chums don't recognize you even if you *did* get them.
I seem to have picked a lot of wrong choices then, I did meet some of them again but it didn't feel like I was having a reunion. None of the really important characters seemed to return for me.
I also did most of the story line with a friend, switching off quests, so it probably killed my chances.