This presentation by Matthew Ellison [Goog docs] given at last year’s Australasian Online Documentation and Content Conference (AODC 2009) has some excellent points on how to craft online help for context sensitive calls. This is something Bentley uses (a lot) and I’m trying to catch up on. There are really a lot of excellent points in these slides. I believe that even if you aren’t employing context-sensitive help, structuring your help as though you were is just as likely to get your users to their answers faster.
Also, the slide in this photo (from the same conference) made me laugh out loud (literally, not in a LOL sort of way).