I think you have to be on Facebook to see Matthew Reidsma’s post on the benefits of online exposure so I’ll excerpt a key bit here:
Here is what that I have learned, even though I had already heard it repeated a thousand times since Tim O’Reilly first wrote it: the problem for any creative type isn’t piracy, it is obscurity. When I stopped posting comics online, my mini comic sales dropped about 60%. Let me repeat that: When I stopped giving away my comics for free online, 60% of the people who had previously given me money to read those same comics on paper stopped giving me money to read them on paper.
UPDATE: the whole post is also at Reidsma’s Livejournal and the whole thing is worth a read.