Well, I've tried the GT's on several cars over the years and can tell you that they generally have a sidewall that's stiffer than the competition, which is good for hard cornering but makes the ride bumpy. I used to feel every little transition in road surface with them. Along with this, they used a sticky rubber compound, which along with the sidewall stiffening helped them have a tremendous time on the +g skidpad tests, but shortened their overall life expectancy.
Basically they were good tires, okay in the rain but not all season, and not great on long trips because they'd wear your backside out.
Now in 2008 Goodyear switched to an entirely new compound on the GT's, along with a more aggressive tread pattern, and now they are selling like hotcakes. If you can ever get one for under $100 it's a good buy. They are now way better in the wet than they used to be, and somewhat marginally better across the road. The old GT's got crappy mileage as they were such a soft/sticky compound. The new one's supposedly have an improved ride and, with care, can reach the 40k mile mark. I never could get more than 26k out of my GT's before.
Anyway, here's a really good write up from an acquaintance, he had me laughing about his review of the GT's, but still stayed fairly neutral throughout.
Speed Sport Life.
Here's a pic of the new GT:
