Embedded in Microsoft’s Bing strategy are four key verticals: Local, Shopping, Health and Travel. Beyond local itself, the other three have strong local elements or dimensions (explicit and implicit). However I would argue of the four Travel (Farecast) is the strongest and most differentiated.
After that I would argue the order goes: Shopping, Health and Local. Bing Maps is very strong but I think the local offering needs more work and differentiation.
In my opinion, Bing Travel may be less of a threat to Google than to Kayak or other travel sites.