I would like to get new versions when they're ready. By making the jump to a paid add-on, you shift expectations. I'm willing to put up with the occasional glitch or bad release from freeware, but if I'm paying for it, it should work. I would like to point out that this is the only add-on I've ever paid for - it was that compelling.
Because of Carbonite's scope, it replaces a lot of specialty add-ons I was using. A buggy Carbonite release is much more likely to shut me down entirely than a buggy specialty release. I do appreciate you leaving previous versions available for download!
I love new features, but please make sure they're stable before a release. The frequency of a release isn't as important to me.