Just watched the demo video. Several times, you refer to Market as a plugin.
Does it work with other themes, or do you have to use the Market theme? The included templates are nice, but I'd like to have a 3-column design on all my pages.
Can I use Market with other themes, or would this require a custom job to get the look I'm going for?
Market is in fact a theme. Much of the demo video talks about the Market Product Manager, which is a plugin created to work along with this theme to make adding products a much easier task than sorting through custom fields. That being said you can still customize the design anyway you want. If you are not great with code, there is also a paypal plugin which will insert a buy now buttons into any post with any theme.