Just had to reinstall Windows 7 on a PC that had a failed hard drive - not a nice experience.
A while ago I purchased the family upgrade pack version of Windows 7 Home Premium. This let me upgrade 3 PCs for ~ £120.
That's the 'Pro' - the 'Con' is that it's an absolute pain reinstalling if you have a hard drive failure because you have to reinstall Windows XP first so that the licence key will work.
This doubles the time needed to reinstall Windows 7 - took about 2 hours in all.
I'm not impressed - Microsoft should sort this.