I use dtSearch Desktop (www.dtsearch.com) as my desktop search engine. Although it is a commercial product, I think it's the best and stable bet, given the rise and fall of many other such offerings (e.g. Google Desktop Search).
Anyhow, I've just upgraded my (MSWindows) plugin to the dtSearch indexer, so as to nicely handle Mathematica notebooks, specifically to avoid indexing and viewing the "junk" inside GraphicsData, CompressedData, and OLEData cells.
If anyone would like to receive this plug-in, it may eventually show up at dtsearch.com, but please feel free to email me your request.