I installed Parallels desktop version of the virtual machine software when I was still on OS Snow Leopard. I installed an extra 4 GB of memory on my Mac giving it a total of 8GB. I built a vm with Win7 SP1 64-bit and have installed Office, SQL Server Developer 2008R2, Visual Studio 2010 Premium and other developer-oriented software.
I typically run the VM in Window mode (not coherence) and whenever it runs my battery goes to zero in a few hours (2-3). When I don’t run it, my battery lasts much longer (an extra 2-4 hours).
Also, it seems like anytime my Mac sleeps, when I wake it and go to my VM, I have no internet connectivity (I’m using the Shared Networking setting) even though my Mac does have internet. It takes several minutes to an hour for network connectivity to resolve.