The art of garage door maintenance and repair seems to be considered voodoo by many people, but I've found them quite easy to work on safely.
I was having the exact same problem 3 years ago with my door - the cables kept jumping the spools. After it happened 4 times in 1 month, I took the time to repair it myself (and I still have all my fingers). The key is to work with the door positioned so the spring tension is near 0 (which is when the door is at the top of its travel). In this position, the cables can be safely wound/unwound from their spools. A properly-located clamp prevents the door from sliding down when you don't want to, and the means to re-adjust the door to run straight and true.
I won't go into details about how I did it, but I will point out something that apparently no one else in the universe does: your garage door should be greased.
I can honestly say in all my life I've never seen a garage door greased, except for mine. I liberally greased all the tracks, every wheel (packed with wheel bearing grease) and every hinge (with white lithium grease).
It's been 3 years with no additional maintenance and the door still glides like nobody's business. Total cost of repair: maybe $3 in grease and about 2 hours of my time.
If the guys who come to fix your door don't grease it (and I doubt they will), I highly recommend you grease it yourself after they leave.
People have told me, "you're not supposed to grease your garage door". No one has ever been able to answer why.
Ryan
