December's supposed to be a month of miracles, and - at least in terms of gaining market share - Google seems to have pulled off a minor one.  New Nielsen stats show that the search giant increased the distance between itself and competitors by a considerable amount.

Nielsen put Google's share of the U.S. search market in November at 65.4 percent.   That number increased to 67.3 percent for December, which works out to a gain of 1.9 percent.  Swings like that aren't without precedent, but tend not to happen on a month-to-month basis.

Yahoo, meanwhile, lost share.  Its numbers slipped from 15.3 percent to 14.4 percent between November and December.  And Bing suffered a similar fate, with Nielsen recording a drop from 15.3 percent to 14.4 percent.

So it looks like it's time to once again ask: how high and low can Google and its competitors' market shares go, respectively?  And is there a point at which Google's gains will work against it?  Opinion pieces about the "Microsoft of search" tend not to be complimentary, after all, and antitrust regulators are already growing uneasy.