There's a good article posted on Peter Rip's (Leapfrog Ventures) blog about the different levers that factor into the business model of a company. Well worth a read.
One of the key levers that is missing from Peter's graphical model is consideration of the sales strategy. This is one lever that isn't adequately thought through in many of the presentations or deal pitches that I see.
Getting to a cost effective, repeatable sales model is one of the biggest levers on the capital requirements of a start up - spend the time thinking about it up front!