Microsoft's six-month old search engine Bing has been performing admirably, says market research firm comScore, and it grew to a 10.3% share of the search market in November.

During the month of November, core US search volume grew by 17.8%, but only Google's and Microsoft's sites increased in share. Yahoo, Ask, and AOL, on the other hand, all declined. So what's driving Bing's growth while its partner Yahoo falters?

Even though it has a strong marketing push behind it, Bing is helped significantly by its placement as the default search engine in the toolbars of new computers. TMT Analyst pointed out earlier this month that Microsoft's distribution deals with OEMs Dell, HP, and Lenovo significantly increase Bing's exposure, constituting around 50% of the consumer PC market.

Many of these toolbar deals formerly belonged to Yahoo, the company's CEO Carol Bartz reportedly said last week.

But toolbar search is only a piece of the puzzle, and really, desktop search isn't all there is. Mobile search is really the place to be moving forward. This is why the Bing iPhone app, released yesterday, is so important to Bing's continued growth.

The Bing iPhone app has already been praised for its elegant interface, voice search integration, turn-by-turn direction capabilities, and location-enhanced results. This is a noteworthy departure from Google mobile for iPhone, which actually required the native Mapping app to be launched separately for location searches and directions.

With apps now on Windows Mobile and iPhone, it's only a matter of time before official Bing apps come to Android, BlackBerry, and webOS for even better mobile search representation.

When Google acquired AdMob in November, Susan Wojcicki, Vice President of Product Management and Vic Gundotra, Vice President of Engineering, said that the mobile Internet is driving an explosion in search. According to Morgan Stanley reports, iPhone and Android have contributed to a 5x expansion of mobile search in just two years. As smartphones become more commonplace among the average consumer, the use of mobile search will only increase.

It's a good place for Bing to set itself up.