WebOS hopefuls -- especially owners of a Palm Pre, Pixi or their Plus variants -- you there? HP's TouchPad launch is a few days away, and the company's seeking to entice loyalists with a $50 mail-in-rebate on the new slate in the US and Canada. You've got until July 31st to make good on the deal, and all it'll take is proof that you own one of the aforesaid phones. Still need help deciding? We've heard that a visit to Walmart might score you some