If you really did a good job of making sure the music that was uploaded wasn't copyrighted, you wouldn't have a business because nobody would be looking for that music. The period between illegal mainstream content going up, and that content coming down, is just long enough for Grooveshark to have a competitive cost advantage over companies who properly license their material from day one.
If the tactics aren't at least "questionable", then why has Universal declared "legal jihad" on Grooveshark?
P.S. My band's music is on your site. I didn't put it there and neither did anybody else with proper authority to do so.