Good uses for virtual machines?

I have VMWare and set up separate virtual machines for each of my projects. Mainly to help keep me focused and to keep everything isolated. For example right now I have separate virtual machines set up like this:

• Autoblogging - All my autoblogs with passwords saved in Firefox and materials such as plugins and PLR articles are kept here
  
• Macros - I have a custom ad posting macro set up so it can run and post ads in the background, while my main non-VM desktop is free for me to do whatever
  
• Proxy access - I have TOR and FoxyProxy set up on this VM so I can do whatever I need to do that requires anonymity or frequent IP changes
  
• Trial software - I use some trial software and created a snapshot of the machine right after I installed them. The intention is to rollback to the snapshot once the software's trial expires. I haven't tested this yet.

That's how my VMs are set up. Does anyone else use virtual machines? What do you use it for?

That's actually a great tip. Us mac guess get the short end of the stick when it comes to tools, both white and black hat. I never thought to split up things in to multiple VM's.