Don't let your web site drive your mission.

I once watched the staff members of a new nonprofit engage in a bitter struggle over the information architecture of their web site - in the hope that this would help them figure out what their mission and organizational structure should be.

Bad idea. The resulting web site sucked, and the nonprofit agency's overall track record isn't so great, either.

You need to think first about what it is you're trying to accomplish, then design your web site around your goals.

Don't put Descartes before the horse.

(Sorry about the feeble philosophical pun.)