Anyone want to estimate how much money they just lost?

Excluding the negative press, let's upper bound what it means to lose 1/48 (= 30 minutes) of one day's revenue. Google's yearly revenue is dominated by search + Adsense. That was about $5.5 billion in Q2 2009 (from Googling "Google revenue") so about $22 billion over all.

Dividing through gives:

(22 * (10^9) dollars) / (365 days * 48 (half hours)/day) = 1 255 707.76 dollars / (half hour)

Hence an upper bound is that Bing lost about $1.3 million dollars for this downtime.

Bing is not doing as much business as Google, that Google number includes all kinds of other things besides search, and it was after 5pm US time (all of which will adjust the number down). Still, an expensive error, and this of course doesn't factor in the negative press.