I'm running Win7 64 bit w/4gb DDR3 RAM. It's working perfectly. I didn't even uninstall the old 2.x Sync. I just turned exited it, so it's not running. HTC Sync 3.x is running and connects every time I asked it to. I'm using OMJ's latest ROM.
What I find cool is that it pulls my photos off my phone to my PC, along with syncing music if I want it to and documents. But honestly, I just needed a good sync that would take my Outlook contacts and calender both ways.
NOTE: The HTC website says it's not for US Customers, or even for the EVO, but I've not had a problem at all. Here is the link:
Application - HTC Sync 3.0 for HTC Legend