first, here's what happens if you try to paint over it: it mixes with the paint and makes a big slubby mess.
different ways to deal with it:
1. excision. cut out the area with a drywall knife and do necessary repairs before painting.
2. partial excision. just cut deep enough to remove the glue, patch it with spackle, COAT the spackle with BIN White or Kilz. then paint finish coat.
if you do not coat spackle with a sealant like Bin or Kilz, you will get a different finish 'color' in paint due to absorption and texture differences. OR
3. Scrape, scrape, sand, sand, wash with TSP.
edit: or did you mean like a widespread area where wallpaper used to be?
in that case it's a major scraping/sanding operation (WEAR NOSEGEAR) followed by many TSP washings. if so, it might be worth it to totally replace the drywall. or if you can find a SAFE solvent to remove the glue that's an alternative.
Last edited by oldkentucky; 04-02-2011 at 08:52 PM.