Feel like I ought to chip in here...
Firstly my motivation to develop and help users has never been money, and the team have very kindly offered this as a 'thank you'. This is a step forward (think future developers and cool apps in the market place) for people to contribute to ClearOS. By providing some financial incentive for the substantial effort it takes, it motivates other developers to also contribute which is ultimately better for ClearOS and users.
Secondly I also understand that the mail server is part of the 'core' ClearOS functionality, and that charging for it seems like a 'feature reduction' or change in the ClearFoundation ethos (regardless of the price)- and because of that I think Pete / Daves suggestion of a Cyrus IMAP solution is a good one. The Market Place should be about choice...
Moving forward if we as a community want the Market Place to thrive will need to consider how we support user contributions (not just mine). The concept that Open Source software should always be free (as in money) is a wrong one. When you buy it you actually own it to hack, pull apart, use however you wish etc. I'm not going to argue the pros/cons of the open source model but there's plenty on the net...
If we want ClearOS to have a vibrant selection of turnkey apps that can be used out of the box, rather than a bunch of hacks / howto's then it needs provide some incentive. For example I have supported the Zarafa app in 5.2 for the last two and a half years, across two threads totalling 160000 views and 1200 posts... that takes time, and I sure hope others don't get put off. Given enough time I could probably write one for SOGo...but would you pay for it?
And yes Ben did pay for the beer

thanks!