It's not spectacular - but (to me anyway) it communicates a cutesy friendliness - the squiggly fonts and child-like primary colors gives a sense of invitation to poke and pry at the system's abilities, and also conveys a sense of wonder.
The bing logo, on the other hand... the font is poorly chosen, IMHO the kerning is all wrong, it feels like something one would whip up in 10 minutes in Paint, not a professional logo. Furthermore, the choices of font gives me the feeling that they're trying to position this thing as hip and cool (hence the bistro comment), where the system is, as of yet, deserving of none such accolades.
For me, the irritation is the panther thingy in the background on search results. It just looks like someone with no design sense found some clip art and decided to put it there.
I didn't understand your comment until I enabled Javascript for the occasion and found that they use photos. And corny ones, too; I'm looking at "Hot air ballons over Cappadocia" (I still don't get the "panther thingy"; maybe because I'm in Germany). Makes no sense at all to me - why would they want to do that?
I'm actually thinking there's room there to make UI improvements that would benefit the user.
For example, with the live id and being logged in, I think it would be neat if these background images eventually ended up being something relevant to me rather than something generic.
Right now, there is definitely room for improvement, but I wouldn't say it's downright bad.
