I just found out that Toys R Us is currently selling the Toy Story 3 sets online!
It states that the items are in stock and ship in 1 to 2 business days from the warehouse; however, after talking to some associates at a local store they have been instructed not to put these sets on shelf until May 1st. Not having completed the transaction online, it may say the same for shipping the online orders too.
Toys R Us does have free shipping on orders over $100, but if you're just looking to pick up a couple of the small to medium sets, then shipping costs can add up.
If Prince of Persia was any indication, then LEGO Shop@Home may pull the trigger soon too!
UPDATE: It looks like there's a crack down on early release. LEGO Stores and TRU's that have been caught putting product out before May 1st, are being told not to do so. So, if you see a set on shelf , pick it up now. Otherwise you'll have to wait a few more days.
Also note that the TRU website has removed the Toy Story 3 sets.