It is my understanding from reading around that the average person’s balance between slow/fast twitch muscle fibers are 50/50. Sprinters have more fast twitch, while marathon runners have more slow twitch. I know that the abs are predominantly slow twitch for everyone, but what about other muscles? Which are predominantly slow/fast?
If you have a good link that will shut me up, that works too. 
Generally speaking (general being the operative). Muscles that are long in nature (fusimform) like the biceps , hamstrings are likely to have a higher percentage of fast fibres. The quads and other muscles that are pennate in nature and suited to developing force at relativley slower speeds are more likely to have less fast fibers in comparison. The only muscles that have a 100% fast twitch fibers are the levator muscles of the eye lid and diaphram muscle (think about how fast you blink and sneeze!). You can compensate for lower fast fiber make up through hypertrophy of fast fibers.
What is interesting is that there are no studies that have biopsy readings of hamstring of sprinters and other prime movers for the sprint (suprise suprise who would like a chunk taken out of their prime movers?). They have taken readings from the calf and quads, which are not the only muscles responsible for fast sprinting.
Abs are actually about 60% fast twitch in most people. There use to be a good study available online that outlined many different muscles. It was available from Curtain University’s web site.
Charlie has covered this in one of his Q&A columns for T-mag. It doesn’t matter what the fiber makeup is unless you’re training for hypertrophy. You still have to train the fast twitch fibers even if you’re predominately slow twitch if you want ot be fast.
Also there was a program on the TV the other day about a canadian kid, don’t remember his name, who ran in 10.55 who had his quads biopsied and found an 85% FT and the rest was either intermediate or ST
bob hayes wasn’t he 50/50 which shocked alot of docs.