Depends on what you consider a "regular basis". Upgrading every 6 months or so, they aren't going to ask questions. Calling every week wanting to re-activate they are going to start asking questions about why.
I even told her that I was putting XP on a 2nd computer for myself. Maybe it was because I had a special OEM version of XP Pro (5 activations before having to call), or she just liked my voice, but she activated it for me. And if one rep refuses, call back and ask another one.