Ok, here is some input from someone who actually HAS a fiberglass hood. They're not that bad. I also heard they make your truck run hotter, but haven't seen any evidence to prove it.
As for the cracking, yes, they can do that. That's part of why I got mine, but if it's not too bad, you can re-glass it pretty easily with some supplies from Lowe's and sanding. A random orbital makes it much easier. Here's my thread from start to finish:
http://www.gmt400.com/forum/showthread.php?5404-Cowl-Hood-Work-in-Progress&highlight=cowl+hood+work
The other thing I like about mine is that the cowl is actually functional. It's completely open underneath, no cross supports like on the steel hoods, it basically has the same shape underneath that it does up top, if you get what I mean.
Now for some of the cons, yes, it probably won't fit quite as nice as a steel hood, but usually they can be made to fit pretty nicely, just takes some tweaking. Yes, they can crack, and it would suck, since you would have to sand, glass, sand, and repaint that area. They are lighter, but if you think that the 40 lbs. is going to make a difference, then you're kidding yourself, it only would matter if you're in serious competition.
I like mine, and I'm glad I got it, I'm not sure if I like the steel hoods better or not, there are certain styling aspects I like better about this one, but there's one more thing that makes a pretty big difference for me. The hood hinge springs. They're stronger so they can hold up a heavier steel hood. I had to take them off mine, because it was bending the hood when I went to close it, and I'm pretty sure they would've ended up cracking it, so now I just prop it up. I've heard you can get weaker springs, or small gas struts, but a prop rod is easy enough for now.