Why are Firefox, GoogleMail and Apache such successful products? One, grossly simplistic answer is that they are not owned by Microsoft. Which is why it's just "Bing" and not "Microsoft Bing" or "Bing [click here to read license agreement before use]".
Bing, while still in its early stages of life, has done pretty well gaining interest and usage from the online community. However, Microsoft wants to get away from just the desktop browser space and is spreading itself in all directions to get more people using the search service.
So, now we have a Bing SDK in Cocoa Framework for Mac and iPhone developers, allowing them to easily add Bing search functions to their apps.
Now, while there may be some Mac developers out there who would consider using a Microsoft product as some sort of deal with the Devil, there are plenty of others who will appreciate that Bing is fresh and new compared to older search properties like Yahoo! and Google.
Licensed under the Microsoft open source Public License, it offers searching on Web, video, image and phonebook data. Searches can be handled synchronously or asynchronously.
The SDK is available on CodePlex and is approaching nearly 1,000 downloads after a couple of days.