Yes, there is some difference from what I have seen … when we first looked at Bing right after SMX Advanced in June at a Microsoft sponsored event – we were able to determine that Bing relied heavily on anchor text and URI architecture … which made it easy to SPAM … I have seen a couple small shift in this in the last month, but it still appears to be working.
I would still optimize for Google first due to the engine’s market share, but definitely keep an eye on Bing – just as you would Yahoo