I must be honest, I havn't heard of any reports here in Sweden (or
anywhere else) that this is a real problem, are there any true incidents
that this has happend?
Yes. If you sit with your laptop in the park across from our office
you can see 3 unprotected wireless domains. There was an article [although
I can't remember what publication] featuring a few people driving through
the City of London [London's financial community area] they found
serveral unprotected LANs.
Just cause there are unprotected WLANs dosn't imply that spammers use
them (perhaps its to hard for the spammers ;)).
Corporations should protect ther WLANs but saying that spamming is a
great threat is to overdo it.