I've been doing a great deal of protoyping and prototype testing lately - surprise.

Last fall, I got to test an extremely high-fidelity rich AJAX app for IntraLinks. This prototype was highly interactive and used to test a number of new design concepts, get internal buy-in, show what could be done, and gauge technical feasibility.

Not too long before that, we built a Flash prototype for a company who wanted to showcase their RFID tracking software. This prototype was used to get internal buy-in and show the concept at trade shows as a marketing tool.

Currently, we're testing a number of prototypes for the LA Times. Some are paper, some are HTML. They too have a number of goals and uses from getting buy-in, to testing design concepts, to seeing if the technology team can build it (or how they will build it).