It seems that compiling a kernel for n810 devices involves a bunch of clean compiles, a little offering to the daimaou and some mules for the purple cat (now that I've included some nice narrow references Lou ;).
Issues don't seem to be related to the kernel image itself being too large, but compiling some functionality just seems to make the kernel kill the boot just before the desktop is displayed. These two pages are a good start along the merry road to a new kernel, even one that actually boots. Anyway, after a bunch of compile, download, try to boot cycles I found that you can have fuse, dm, encrypted filesystems, NFS client + server and xfs in a working kernel. I'm still trying to work out what parts of iptables state based filtering makes the kernel crap out.
But with the fuse and crypt stuff I should be able to have some fun making a nice front end to encrypt the internal 2gb sdcard... it will be interesting to see how much crypto impacts performance. I think /usr can be raw, but a bunch of the stuff in /home should be encrypted just because I don't want the guy who steals my n810 to read my email too ;-p
In other news, it sort of feels a little like the start of fight club, but instead of browsing furniture and other crap its hardware. 10G-BaseT can not arrive soon enough.