I cycled my tank with live rock. You'll be pleasantly surprised with the process... it's actually pretty fun, watching the creatures emerge and algae grow. I waited a week and 4 days and added hermit crabs and astrea snails. Then I waited another week and 4 days (thereabout) and got my clownfish.
Like everybody else, I highly, highly recommend cycling with live rock. Honestly, it's the only way to go. I know it sounds boring, as freshwater fishless cycling is boring (one of the reasons I don't do it and don't recommend it to friends), but marine is a whole different ball game. It really is the most effective way to go about getting your tank ready for fish and inverts.
Check out Camaro's sticky on the foundations of live rock at the top of the forum for more indepth info.