Save files: You can use IanM's plugin to easily find standard system folders such as "My Documents" and "AppData" which are ideal for creating files at runtime. All of my games use this method and it works fine.
Juney thanks for the extra info on installers. Didn't realise they'd relaxed the rules there...
_Pauli_ glad to have you aboard! Will you be publishing "Colony Defender"? It's a great game
In answer to your questions:
1) Yes, but you would have to pay $99 per year to keep your game/s on the store if / when they introduce the fee. My advice is get in early to see if your game will cover the cost...
2) ...see 1
3) I'm working on a simple guide more or less as published in the newsletter. The main difference is the code you would need for using the AppUp SDK. I can give you some of this as I have the code for the dll we use in DBP so I guess I might be able to add some help for DGDK. If anyone out there already published using DGDK it would be nice if they could share their experience so that I can include some code in the guide / newsletter.
4) Paypal is the standard method of payment at this time but if it's a real problem you could try contacting the support team through the Developer forums.
5) Any games you sell on AppUp you still own all the rights to and you can sell elsewhere or even give it away. The only thing you can't do is advertise the other places you sell your game from from within your game on AppUp.
Regarding Code Signing if anyone else has any objections to this please post them here so I can get a petition filled with comments from developers here...