Yup, a few people that I've done deals through
UO-Auction with. Would meet 'em in game for the sale, and during the whole process I'd ended up putting them on ICQ, and ever since then they'd harass me on ICQ regularly. Nothing terribly bad, just the usual chatting up and refusing to go away.
Purely in game, griefers who won't leave you alone are too many to mention. Luckily they usually vanish after a while.