This is really neat!
Michael Tapes (WhiBal) and Imagenomic (Noiseware) have created a utility (for both Macintosh and Windows) that extracts the embedded JPEG -- either from individual RAW files or from all the RAW files in a directory.
Michael Tapes explains the utility here:
IJFR supports almost all raw formats including DNG. Some cameras that we missed are Canon 50D, all Sony .arw, and Canon sRaw. We do not support medium format digital files, although someone has asked me to look into supporting Phase One files.
You can download it from this page (registration required).
Initially I shot RAW+JPEG with my D300 but switched to shooting only RAW when I realized that I hardly ever used the JPEGs. On the rare occasions I needed JPEGs, I could export them from Lightroom. This utility makes it even easier.