Given the cross-platform applications and near-universal web, I currently have no version of Windows installed on a Mac. I had previously used VPC5 on an iBook G3 to run Win2K Pro, which I mostly used with Office. It worked fine but I don't have it installed right now since my iBook only has a 6GB drive and I'm in the midst of a massive project on that computer.
Part of me wants to get Windows 7 running on my Santa Rosa MacBook, but I'd probably only do it out of necessity (that is, if I needed Windows-specific applications for work, development, etc). I find I don't really miss having the option of running Windows around unless I get some tough Office file which won't open with Office for Mac or another program, and even then, I find many more files with fancy formatting are coming to me in PDF format these days (I send most of mine that way too). I do know it would be a better option than purchasing a Windows laptop, however--I already own the hardware and would simply need the software end of the solution. (Budget PC laptops aren't worth it due to the amounts of shovelware installed).
To give a "like" or "dislike" vote, I'm going to say I like the idea, but would only use it out of necessity (i.e. if I was required to use a Windows-specific application).