It isn't a problem for me, since I'm not a high value target for spam. The other reason is that I've raised the bar by a very tiny amount. CAPTCHAs (those type the letters in the picture tests) are designed to raise the bar for spammers, and I've got kind of a unique one on this blog.
My comments aren't hosted on blogspot, but rather on a site called haloscan. That tiny little difference has meant that I have never displayed a single comment spam ever. Automated comment spam occasionally is done, but it is always done using the normal blogspot comment fields. I get notices of these when they happen, but they aren't a worry because they aren't displayed ever or crawled by search engines.
This works because spam is a problem of economics. It takes very little work to be not worth the effort.
This is also a reason that firefox tends to be more secure than ie6. Fewer folks use it and therefore its less lucrative to write firefox exploits. So one of the surprising things that would tend to make ie6 and the web more secure is if opera, safari, and firefox took off!