I too am still experiencing this issue even in Win 7 RTM 64 Bit. I downloaded the ShellExView app (64 Bit version) and executed it. There are about 150 items that display about 4 or 5 are red. One note, you may have to Run as administrator to be able to enable or disable extensions. I didn't see any that should be potent enough to cause Explorer to hang; the only odd balls were AVG, Adobe Elements (Context Menu), Bluewire General Property Sheet, GraphicsShellExt Class and PowerISO. I can always tell when its hung when I try to double click on an icon on the desktop and it won't function. I end up going to Task Manager, doing an End Process on explorer.exe, then do a File->New Task (Run..) and type in explorer to start up again.
Additionally, explorer.exe is soaking up a lot of memory. Every time I look at the memory usage during these hangs it's typically 600k+. Even after a restart, it will start small and gradually go back up to 300-400k+ then eventually reach 600k+. It has topped at 705k+. What could cause this? Could beta drivers cause explorer.exe to do this. In all my years of being at the bleeding edge, I have never seen explorer.exe do this.
I also have Win 7E RTM 32bit installed on a different machine. It does not exhibit these issues.