Mike - it's been a couple years but I believe in a lot of cases I had to replace one by one. It's because companies with both 32 and 64 versions frequently have different .dll file names. They have to to keeps things straight. The whole process was a royal pain but in the end totally worth it.

 
I had no idea some companies made this process so difficult. My transition experience was the opposite of yours - and even now I can move a project between a 32 bit XP machine or a 64 bit Windows 7 machine without any problems. It's all seamless here.
 
However - I don't have 100's of plugins, just a handful of my favorites. Maybe that's why I've been so lucky.