I've recently seen the light and converted to Mac's but my business software only runs on Windows so I use Parallels virtually daily for those Windows specific tasks that I need to deal with. I can also vouch for its stability etc, and being able to switch between Windows and Mac without having to reboot is great. Simple to use too. As far as virus' etc, as you will be operating within a Windows environnment, to the extent that you expose yourself to the "outside world" via email/internet etc there is still that Windows risk that you don't have on your Mac. So you should protect yourself within Parallels (Windows) but from what I understand due to the "virtual" environment it shouldn't impact on your Mac environment.

Hope that helps

Kim