I've seen several programming guides for the 2.6 kernel but linux is up to 3.11 now. Are the differences between the kernels so much the 2.6 guides are unusable?

Linux kernel is upto 4.0 now. There was just a version change from 2.6.x to 3.x to 4.x. So there may be not big changes. But some interfaces might have changed. Depends on what you want to work with. Still if you get the working of the kernel then adapting would be easy.

Moved: This thread is more suitable in <Linux-Kernel> and has been moved accordingly to help your thread/question get the exposure it deserves.

I would say ... "Yes, maybe. Look and see."

The Kernel is one of the most-rapidly evolving areas of the overall Linux system, because (of course) it is always striving to be on the cutting-edge ... of the latest versions of ... the ever-growing number of CPU-types that it supports. ("Everything from mainframes to microwave ovens" is not an understatement.)

"Good kernel-programming guides" are always excellent things to accumulate on your bookshelf read ("again and again until the pages fall off"), but always bear in mind that they are, necessarily, dated. Supplement your learning with a careful examination of the kernel source, and of the plethora of on-line sources that discuss the voodoo mysteries of vagaries of each particular kernel implementation. "There is always something else out there to keep you on your toes!™"