I also have experimented with using meta tags and I found a "gotcha" if you plan to burn docs to CD - the CD file system doesn't support the meta information! (as I found out the hardway 6 months ago). I'm not sure about DVD burners. In any case, make sure to test this before you commit to meta tags.
As far as scanning/database programs, nobody has mentioned Paperport in this thread - it does an excellent job and can OCR keywords from documnents in the background.
I agree with the 150dpi recommendation ... it's the best combination of scanning speed and acceptable legibility for most documents. However, OCR works best with at least 300dpi, so I use this setting when I need to extract as much text from a document as possible.