currently I'm using Sandboxie on my Vista 32 bit system. I don't realy use it for security, but for an application that allows only one instance to run (Scia Engineer). It allows me to create multiple instances of the program, each instance in it's own sandbox.
Now I read that Sandboxie doesn't run in Vista 64 bit, due to another Kernel protection or something like that. People tell me it's not realy a problem since IE7 already runs in sandboxed mode... But that's not what I need :-)