I briefly considered the implications of a similar service which would gather checklists of important dates for small businesses. For example, tax return filing dates, sales tax quarterly payments, business license renewal dates, etc.

The rough idea was that you would collect this public information, add a calendar/reminder component and then localize (which would be the hard part).

It sounds as if you may be going down this path at some point in the future. If so, I think it would be a very interesting service for which small businesses might pay a token yearly fee.