The worst of these blogs post entire albums, steal onesheet copy, utilize free hosting services (against the terms of service of those services incidentally) and then rake in advertising dollars as the hit rates go up.
Verbatim (that's my new unhip way of saying "Word") to that.
Not really looking to get into the morality discussion, or the "what blogs can and can't do, what's a blog's real function, etc" one. We can take for granted that upping a new album from a living, breathing artist who supports himself off this stuff or wants to--that's pretty shitty, even if you disclaim that "All music posted here is for a 24 hour testing period. It is not my responsibility to make sure that you follow these rules, it is your own. I will not be held accountable."
MP3song blogs can rationalize teasing an album, drumming up interest, etc. The best of them have focus past NEW SHIT NEW SHIT, either curating old with new or taking advantage of the internet's collective memory to preserve some random seven-inch or mixtape freestyle nobody will remember if someone doesn't decide it should be.
However, Sylvester also posits that this will lead to even shorter cycle lives for albums that deserve a longer "listening period" - I'm not sure I totally agree with that. Of course, Sylvester likes mostly shitty music so maybe the short life span he worries about has to do with that. No, good albums were "lost" just as much in the 60's as they are today. Eventually the shitty stuff gets flushed or turned into an object of nostalgic derision.
UPDATE (8:11 PM): Nick has taken down the link to Aquarium Drunkard's hit rate page...