Not Just A Pretty Girl compares the business models of Diaryland and Six Apart: Diaryland versus Movable Type:
An interesting corollary to the Dairyland situation is the relationship between Movable Type, Movable Type Pro and TypePad. I’m an extremely happy MT user. I love MT. I think it’s the best thing ever. And it’s free. I made a donation to Ben and Mena right after I started using it, but my donation didn’t unlock special features of MT. I’m not going to be getting any extra special features in the next major release of MT because I did donate. All the features are there, and will continue to be there, whether I donate or not. And even though they are in the process of launching a pay product, they’re not going to stop supporting their free product, and in fact, are going to continue developing it (that’s my understanding, anyways). When the Pro version of MT comes out, I expect that it will have functionality that the free package won’t, but I also expect it will be made clear what features will be in the free version as opposed to the Pro version. And I would hope that there would be improvements and additions to the free version as well, that it doesn’t become frozen in time.