I switched to Macs maybe eight years ago or so, largely because of my wife: she's an astronomer and the observatory that she's at uses linux as their core with Macs as their workstations. I definitely agree with your colleague, I've found that Windows under Parallels is extremely stable, more stable than I've experienced on dedicated hardware, and I would imagine more so if you were running it under Bootcamp, which I haven't done yet.
I have two complaints about Parallels. First, they don't support fooling the OS in to perceiving different video cards so you can run old games under it, second they are very aggressive about planned obsolescence when a new Mac OS comes out, i.e. every year, or a new Windows OS comes out, every couple of years. As a result, I only upgrade when I absolutely must, and I expect Win 7 to have pretty long legs.