Overall application idea is great and very useful for any service based company. Although there are many things that would need to change or be added to make it that much more appealing.
-First of all, the websites design needs some work. I find it to be plain, unappealing and untrustworthy. With a brighter design, you can attract a lot more users. Maybe try choosing some main accent colors and applying them throughout the application.
-From a Developers point of view, the application runs very smoothly. Solid programming but missing a lot of features.
-I would concentrate on adding Google Cal syncing capabilities. I understand that it has already been mentioned but its too important to pass on. Many service companies use Google Apps to organize their scheduling. This would make things a lot easier for any user. Maybe even integrate with other project management applications such as Basecamp or any other.
-For the booking process, I think you should also ask the most information possible from the client. This will make things easier for the company to contact the user.
-The domain name is simple and easy to remember, but I would try to find a shorter abbreviated version to host the users apps.
-You could also allow the registered users to insert their custom logo for a small one time fee.
-For future consideration, maybe even add an advanced payment ability. Allowing the clients to pay by credit card in advanced and send the payment directly to the company (Paypal, Authorize.net etc.) You can also charge a small percentage of the transaction as commission.
Overall great idea. Keep up the good work! Good luck!