Microsoft's previous search engines ( MSN Search and Live Search ), have suffered from a very slow and very small index. Now, unfortunately, Bing has followed suit. Although Bing has a lot of great and funky new features, the index size is still a problem.
Microsoft does seem to have a few tricks up their sleeves though. A new strategy which involves prettifying search results, and focusing on social networking, may just well be the answer to the changing state of the web.
MSN search and Live Search have suffered from a very small index that is updated very slowly, unfortunately, the same is true with Bing.