kernel.org source compatibility
 

Can I use the kernel.org source for debian or do I need to get it with apt-get?

you *can* but it depends what you really want to do with it. You'd need to build the config from scratch, and would miss a lot of customization that the Debian project add, but other than that, you should be fine.

I almost always run self-compiled kernels from kernel.org. I am currently on 2.6.30.2 on my laptop. On 2.6.29.4 on my desktop - but this is due to fglrx issues I haven't gone higher.

I have installed a source kernel - there are instructions on creating a deb file from a source kernel and using your previous .config file so you only have to worry about the new stuff in there.