We appreciate your donations very much- they help a lot.
We're hesitant to charge people for anything unless it's absolutely necessary; we'd like the service to remain free if at all possible, and if people want to donate (as you've done), then they can....we just don't want a few dollars to be a barrier to the usefulness of the service.
Depending on how fast things grow, we may be forced to charge for the service someday, but not yet (and hopefully never).
I would probably have paid $50/year for a subscription to this service. That is why I have made a couple of donations. You have almost completely solve my BB spam problem.