Google and AOL are up while Yahoo!, Bing and Ask.com are down from November in Nielsen's December 2009 search rankings. But let's face it, AOL is fueled by Google, so pretty much all of the gains belong to Google.
NOV. 2009 STATS:
The bottom line is that as always Google gets the lions share of the traffic. Yet both Yahoo and Bing get a fair share of traffic and can't be totally overlooked. Yet if want to promote your site, Google is the key, both organically and using their pay per click Adwords program.