Spam blogs are a pain for both bloggers and blog readers. Blog comments can get swamped with crap and "splogs" clog up search engines and directories.
Bloggers can use word verification or equivalent to stop automated spam comments. One thing they shouldn't do is link to the splog and write something like "I hate these spam blogs! Avoid www.spamblog.blogspot.com!!". This just helps the spammers.
If you do find a spam blog you can report it to search engines and blog services.
Google has page called Report a Spam Result. Other services should have something similar.
Many Blogger blogs have a "flag blog" button in the Navbar at the top of each page. Visitors can "flag" a spam blog and when it is reviewed it will be deleted.
"Flagging" works if the navbar hasn't been deleted or the blog doesn't redirect the visitor to another site. If either of these is a problem visit "Report a spam blog".
Note: Blogger's automated spam catching features can cause problems. This happened to me and it took a while to fix.