All of these reports look like AGP driver bugs to me. The first two are SiS
chipsets resulting in hangs. The third is a newer VIA AGPv3 chipset with a v3
card, with visible agp issues in the dmesg ("Putting AGP V3 device at
0000:00:00.0 into 0x mode"). I would suggest that these issues get reported to
the linux kernel bugzilla.
All of these reports look like AGP driver bugs to me. The first two are SiS
chipsets resulting in hangs. The third is a newer VIA AGPv3 chipset with a v3
card, with visible agp issues in the dmesg ("Putting AGP V3 device at
0000:00:00.0 into 0x mode"). I would suggest that these issues get reported to
the linux kernel bugzilla.