Don Park thinks spam is killing email, and he may be right:
I used to feel comfortable with reliability of e-mails. When I send something to somebody, I felt reasonably sure that it will be delivered and read. That is no longer true today even with wide use of spam filters. When I send an e-mail now, I no longer feel sure of it being read by the receipient.
He goes on to discuss the ins and outs of how he classifies email that makes it through his filters; suffice to say that the volume is still high enough that a lot gets blown away with barrely a glance.
I actually don't use a spam filer; instead, I have filters for all my mail lists and people I expectmail from, and that all gets organized into folders. What's left in inbox is almost all spam, and gets manually deleted without a lot of detailed scanning. This is dangerous though - as the Product Manager for Cincom Smalltalk, I get a fair number of mails from people I don't know and have never met - more than once I've had to scan back through the trash for mails I deleted. I don't have any faith at all in digital signatures; I'me sure the spammers will find a way through that as well. Email, once a highly useful tool for communication, is getting more and more like regular mail every day...