I've never had an issue. I call, they hand out the activation. If they get "testy" with the person on the line, I can imagine there being an issue, but I've yet to meet a person who was shut off.
If they truly have a license to said OS and get shut out, then take it to SLASHDOT and make a lot of noise there.
A friend of mine recently has had a number of problems with XP in regards to needing to re format his hard drive to solve some serious issues.
Now he has been informed he must reactivate the XP license in 30 days. Its down to 23 and the clock is ticking. Any suggestions here as he is frustrated dealing with Microsoft over the phone.