Kernel 2.6 no longer has the khttp server. I have read it in the ChangeLog and in deed there is no option for this in the config. Can't find the actual source, but this may help:
"The kHTTPd daemon which allowed the kernel to serve web pages directly has also been removed as most of the performance bottlenecks that prevented Apache, Zeus, et. al. from reaching kernel speeds have been resolved."
I had kernel 2.6.4 running on my devel server for about a month; no problems what so ever, but this server is not exactly stressed out (it's LAN access only). I did notice the task scheduler improvements though -- it's an older PIII and under high load the interactivity is better than with the 2.4 kernel.
So overall I think 2.6 is good for mission un-critical servers, but I'm not convinced enough to put it on my production servers yet.
I've setup several dozen servers with 2.6 kernels. They have worked well for me. The only problem I've run into is with some users running JBoss (java) servers.
There have been a few benchmarks (google may find them for you) that show 2.6 is ~ 25% faster at web serving than 2.4. Plus it scales with higher numbers of threads. Plus it better handles lots of processes all doing I/O.
I'll need to have my servers running for a couple of more months before I can conclude how much of an improvement they've made in my setup. But the performance so far has been encouraging.