I've been thinking about joining it and I'm thinking about finally filling out the application. The website makes it seem all great, but that could just be a strategy for recruiting more members. So, I'd like to know what it's like from someone who knows what it's really like.
I'm in the Reserves - not the National Guard, but the schedule and training are often along the same lines.
Keep your expectations in check. You'll see a lot of awesome pictures and other such things on their recruiting ads - and you -can- get into some of those things (if you're motivated and push hard to get into those outfits), but you're mostly going to be doing a lot of paperwork and "yes, I'm still alive and fit to report for duty in the event of a natural disaster or some war fighting effort."
That said - the National Guard is state-run. You are probably safer joining that than the federal military, at this point. The Military is going to be cut in half (manpower-wise) in the next five years. Attrition is ridiculously high and it's only going to get worse. The National Guard will probably end up under manpower increases (funding from the feds, ironically enough, for homeland security purposes; though the NG will still probably be doing a considerable number of deployments to Afghanistan).
Just don't plan on dropping your civilian career, completely. It can, however, help you with some networking to get into a career field with better advancement opportunities and other things.