Sometimes what appears in the snippet doesn't contain a keyword but is something I'd like to read around on the page. At the moment searching through the cache to try and find it seems to be the best way.
On a similar note it would sometimes be useful to know where the snippet is from. Is it the meta description, is it from meta keywords, is it extracted from text on the page. Plus if it is extracted from the page, how many locations is it from.
Maybe this feature exists in other search engines. It's highly unlikely that anyone will ever know though, because no one (well it seems that way) uses them any more.