For me personally, I wouldn't enjoy that month. The main reason would be purely selfish. I know that my idea and implementation could make money and instead of releasing it on my own and profiting, it would become property of the company. I would also feel pigeon-holed into working on stuff that the company already does or in the same realm (which in my case is Business Intelligence tools to work with Cognos) which, while interesting, is not where my interests lie which would also limit my creativity.
It should be interesting to see what comes out of 37Signals in the next 6 months to a year.