aakk9999 - 1:49 am on Dec 1, 2010 (gmt 0)
I do not use the "no snippet" meta tag. Nor do I block any bots (good or bad) but my site does not show a preview for some reason. Bummer.
Are you by any chances blocking css in robots.txt? This was the reason with one site I know of and unblocking css did the trick.