I've been using arjanv's
2.6 kernels for a while. The latest ones (2.6.3-2.1.188 and 2.6.3-2.1.189) will not load into the kernel:
nvidia: version magic '2.6.3-2.1.189 686 gcc-3.3' should be '2.6.3-2.1.189 686 gcc-3.4'
insmod: error inserting './usr/src/nv/nvidia.ko': -1 Invalid module format
This is on Fedora Core 2 Test 1 and with 5336 nvidia drivers. The drivers worked fine with 2.6.2-1.177.
They've changed the gcc version they're using to compile the kernel and don't seem to care what it affects.