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I've seen many topics concerning the Google Snippet and there really is no way to control it. Unless of course your design is all graphics and the only thing for Google to index is your META description which has been known to happen.
I have noticed that if certain presentational elements are the first tag after the <body> tag, that those become the first line in the sippet. It doesn't happen all of the time, but I see it quite a bit. The user's search query pretty much controls the snippet.
On one site I'm involved with, a "thanks to our sponsors" note keeps coming up with our most popular search term, and it's on my list of things to do to turn that into a graphic.