This is no more than speculation, based largely on other speculation, itself based on an indescriminate statement Bill Gates made recently (as reported by CNET news) which may or may not have indicated that the next version of Windows could be shipping ahead of its projected 2010 delivery date.
7, in any event, is unlikely to slip as badly as Vista did, so those rolling their eyes at the 2010 date itself can stop already. Microsoft is sure to realize that another performance of that sort will start to set customers to serious questioning as to whether or not Windows is the best platform for their continued and stable operations. Also, the agile bug is really starting to bite over in Redmond, and the general philosophy of "ship early, ship often" is probably starting to make its way up the chain. Getting a minimalist version out so that customers can provide immediate feedback is a valuable approach, especially since the company has clearly lost track of what its customers need.
Either way, the timeline between XP's demise (June of this year) and the potential roll-out of 7 next year provides a window of opportunity for Vista skeptics. Stock up on XP licensing for a 12 to 24 month period and skip Vista entirely (as many people skipped Windows Me) in favor of Windows 7. That's a gamble, of course, but perhaps a good one. Even allowing for a year of tweaking and testing and letting other early adopters find the pitfalls, many organizations have the potential to save a considerable amount of money by skipping one upgrade cycle with Windows.
This is, of course, why Microsoft hastened to deny that Bill meant to say anything at all, because money that you save on Vista is money they don't earn on Vista. Whether you place any value on the information or not, the delay is worth considering if you have already delayed Vista adoption and not found it too painful. 2010 is only a year behind 2009, after all.