I have had a FoodSaver Vac550 since late 2000, I think. We use it several times a week, mostly to prepare foods bought in bulk for freezing. It has vacuum-sealed all of the meat from 8 whitetail deer, 1/2 a pig, large quantities of beef, tons of chickens that I buy whole and cut up, etc. We now buy bags at Walmart, they have a cheaper brand which has worked great for us. We re-use all of the bags after they are washed and sanitized. I agree with Sarah that cutting bags long is a must if you want to re-use them. I'd also say that you'd want them long enough to sit in a cozy whilst rehydrating, since you can't re-close them like zip bags.
I've used commercial vacuum-sealing machines, and yes, for the 10 grand they cost, they do a better job, faster. But for under 200 bucks you can't go wrong. I'd stick with an established brand, like Foodsaver, etc.
I've packaged some food for backpacking, and had good luck with it. Overall, it's one of the few of many, many appliances that I've had that have lived up to the hype that is associated with them, especially if they have their own infomercial. I'd say they're well worth the money, and limited only by your own creativity. They really do help to preserve food better, and if you're only going to use the bags once, it's still cheaper than buying pre-made food. Plus, you know what's in your food!
PS- Sarah's book(s) are a must if you don't already have them, so many great ideas! That's what got me started on really making my own complete meals for trips. Can you tell I'm a fan? :)