I've been wondering this too, since my old Bell Sport needs replacing (I've used it at least 60 weekends, so it doesn't owe me anything
)
Here's what it says on the Snell Foundation website:
Snell 2010 Standards Transition Scheme
The transition from the 2005 standards to M, SA and K 2010 will be more difficult than in previous standards revisions. In general, certification to the new standard will not assure that the same model also meets the requirements of the previous standard. Furthermore, many of the 2005 certified models will require extensive modification to meet Snell 2010 standards. For these reasons, the Foundation proposes a longer transition period. M2010, SA2010 and K2010 will begin a year early. The first units may be offered for sale as early as October 1, 2009. And M2005, SA2005 and K2005 will continue for a year longer than usual. Manufacturers will not be required to stop production of these helmets until March 31, 2012.
~Snell 2010 Link~
Saferacer has the ~Bell Sport~ for $259 and free shipping so I'll probably buy that.