Jay Cutler said he aims for 120-180 but I find that I don't feel that well run it runs high, although that may also be b/c I'm sort of high-strung about my BG? I think that your body needs some "fuel" (e.g. the 3 brands of gatorade, G1, G2, G3??) and I'd rather have some fast acting, "short" carbs "on board" instead of "eating" the tail of lunch although really, I think that some of both is good.
A lot of runners use that "Gu" and other brands of gels but I've noted most of them use maltodextrose that "deploys" slowly. If I have one 7 miles into a half-marathon when they are passing out "freebies", my bg spikes after the race (I run about 2 hours for that distance?).
I am not a scientist or doctor or anything like that but in my (2 years of running that my control has been generally pretty good, with adventures, of course!), I've found that I feel like I run best with more frequent, small doses of fast-acting carbs than "one big hump" and burn it off. I had one run where my pump failed last summer and another one where two sites sweated off (it was really hot, but not Austin hot...) and both times, when my BG got elevated, I felt like crap and had a really hard time running, a lot of cramps.