From an article on CNET about Yahoo blocking Trillian:

IM spam, commonly referred to as "spim," has been flagged by experts as a growing problem. However, experts have also written off spim as a far cry from e-mail spam, which has caused enormous headaches for consumers and businesses alike. [CNET.com]

SPIM? I have to say this is one of the lamer terms I've heard. If you look at the origin of the term spam, it doesn't even seem to come from email at all. So I guess that means for email we should be calling it 'spem'.