I started getting underarm-type hair around them at around age 30. I pluck them when I see them but they seem to spring out when I'm not looking. DH finds this hilarious.
I thought it was just me but then he and DD were watching the celebrity SAS program and one of the contestants was showing her hairy boobs to another woman. It turns out I'm not the only hirsute one, hooray! Now I'm interested to know how common this is via a completely unscientific MN poll.