is it possible that hardware support decreased from kern 2.4 to 2.6? (and other kern
 

I have some computers that their NICs (ethernet 10/100) work with 2.4 kernel but not with 2.6. I also had a 2.6.7 machine eat the filesystem. And I heard the odd numbering for test kernels (2.3, 2.5) has been discontiued, so how do you know what's stable? Monitor support also seems worse with 2.6 than 2.4.

What is going on?

judging by the chatter on the lkml there are lots of things broken in 2.6. i have 2 linksys pcmcia cards that are totally useless under 2.6

true. Why do this though, should I contact Linus ;)

There really aren't that many things broken in 2.6 -- I read the kernel mailing list too, and stuff does tend to break in the development versions, but the releases are mostly OK. Also, depending on how your kernel is configured, some hardware support might not be present. If that's the case, compile the required kernel module and modprobe it on in, and you should be set.