Wink is spot-on. Since it looks like we're in for the proverbial "long war", and intel will continue to be a high demand designator, there will be the opportunity for Reservists to find active duty opportunities. Like Wink said, though, it's exactly like being a contract employee - you would go from one set of recall orders to another. You might take a 3-year Presidential Recall, and then have to look for a series of 179 day ADSW orders. That's not necessarily a bad thing though, especially if you find out that "hey, this "war" thing isn't all it's cracked up to be." I don't know how hard it would be to request augmentation to full-time active duty, but I think it's not easy. Making a career out of being a recalled Reservist might be a hard row to hoe.
You do have to be careful for what you ask for, though - when I joined the Navy in the late 90s, the Navy Reserve was more or less just like Homer Simpson called it - America's 17th line of defense, between the Mississippi National Guard and the League of Women Voters. These days, it's a different story. You want 1 year in Iraq as an IA? You can have it in a heart beat. Involuntary mobilizations are still not common, but the Magic 8-Ball says "Future unclear, check again later" on this. I joined because I wanted an opportunity to get some operational experience, and jeez have I gotten that in spades...