Starting an application for the first time can be a very busy time:

• Display some kind of end user licence agreement.
• Display a registration or shareware usage restrictions dialog.
• Ask the user if he allows automatic update checking.

I’d prefere to have everything in one, very clean designed window. But I think this is simply too much content for one window. This is the current design of the registration dialog:

I like it so far. When running for the first time the standard sparkle dialog will pop up too, but I think this shouldn’t be much of a problem. The next thing will be to find a suitable place for the EULA.