Have you used SFML, would you please provide your honest feedback on using it?
I really like SFML. It's a well designed API, it's well documented, and I find it very easy to use.
What if I spend a ton of time using it, then they don't support it anymore am I basically screwed? I guess I'm basically concerned about the future of it.
This isn't very important. Even if support for it stops, the libraries will keep working, they just won't be updated. If you're looking for an API that will be continuously supported until you die, then programming isn't for you because there's no reason to believe that there will be an eternal anything. Plus, the skills you learn will be broadly transferrable to other APIs, and learning a new one won't be so tough that you should trade SFML for it now (plus, you have no guarantee of never-ending support for that alternative either).
I don't see how they make revenue from SFML as it appears free? What's keeping it from collapsing or not being maintained
It's not a revenue-focused effort. Laurent (the developer) likes coding and maintains the code base largely on his own for his own purposes. It isn't his career.
Will games programmed in SFML work with on Windows RT?
No idea. A question this specific is probably best investigated at the SFML site's forum. If it isn't covered there already, Laurent will get back to you on it in no time.
SFML vs. GDI+? Seems like GDI+ is harder, but I already know GDI well, and seems like GDI+ has a solid future, would it make more sense for me to stick with GDI+?
It makes sense to stick with what you know unless you either want to learn something new or need a feature that what you already know doesn't have. If you know and are skilled with GDI+, what are your reasons for looking for something else? Answering this will help you figure out what to do now, but I'll mention that it never hurts to be able to use multiple resources.
You can't tell the future of GDI+ any better than SFML, so don't worry about how solid you imagine the future of either to be.
Not SFML question but I’ll ask here anyways, I know Poser already, what other program(s) are generally used to make nice smooth looking graphics like in Angry Birds or Cut the Rope or is this really just the artist being great and using any program?
I know that Photoshop, Illustrator, and GIMP are all popular. But I think that you're right in that it's more about the artist being skilled and knowing how to use a given program than any program being "better" than others.
Does SFML support touch screen? Can it be encorporated?
Another good question to ask Laurent, if it's not already on the forums.