I just heard from an inside source that the "Big Sibley" is being updated...but we'll all have to sit tight for a while. The new edition is expected to be released in Spring 2013.
In the meantime we can all continue to enjoy our other guides like Stokes, Crossley, NatGeo6, and Kaufman. Funny thing is, I don't see them as competition for each other. I like 'em all for various reason.