I like it when people tell me happy birthday (on my birthday
![Wink ;)](http://forum.x86labs.org/Smileys/default/wink.gif)
), but telling people that it is your birthday or that your birthday is approaching is like saying 'I expect you to wish me a happy birthday on this day, it is now your duty' which completly destroys the happy feeling received from someone telling you happy birthday. The same goes for chain-"Happy Birthday"'s. If its not sincere I'd rather not hear it at all (not to be pretentious, its just meaningless for both parties).
Disclaimer: I'm referring only to a group of peers that spend enough time with each other to actually know each others birthdays. I don't think the above applies in a professional or impersonal environment.