My wife (teacher) needs Windows occasionally, mainly for report cards, because her stupid school board requires Internet Explorer for some ridiculous ActiveX stuff. (Also, their email system doesn't even support IMAP or POP3, so she has to use Outlook webmail...)

I still have an old XP partition on one of my desktops, I setup a VirtualBox Windows install on her laptop, and her mom has a lightly used Windows netbook... so she gets by with switching to one of those machines a few times a year when she needs IE. If it were a more regular thing, it might be more of a problem...

(Also, the work machines have Windows too I guess... so it's only when she needs to do some stupid IE only thing from home that it becomes an issue with her own computers.)