I have – after some messy hacking – managed to get the Raspberry Pi updated to kernel 3.8.0..

Raspberry Pi VNC window, running kernel 3.8.0..

The starting point was the 3.7.1 Pi code, at https://github.com/Olipro/linux-RPi.    The kernel.org patch for 3.8.0 assumes the code base is 3.7.0, so I had to ‘revert’ the 3.7.1 patch.    The ‘incremental’ patches at kernel.org start with the 3.7.1 – to 3.7.2 patch, but the 3.7.0 to 3.7.1 patch can be found in the main kernel tree, at http://www.kernel.org/pub/linux/kernel/v3.0/patch-3.7.1.bz2    Then ‘revert’ the patch, by appending the -R parameter..

That will give you a 3.7.0 version of the Pi kernel/module/drivers code, so then apply the standard 3.8 kernel.org patch from ftp://ftp.kernel.org/pub/linux/kernel/v3.0/   to update it to 3.8.0..     This will not apply 100% cleanly, so more hacking needs to be done, to get it to compile without errors!

In drivers/mmc/host,
Remove all references to __devinit and __devexit from sdhci-bcm2708.c (as they have gone, since 3.8..)
and change line 1365 from
.remove      = __devexit_p (sdhci_bcm2708_remove),
to
.remove      = sdhci_bcm2708_remove,

Replace the 3.8 version of smsc95xx.c and smsc95xx.h with the 3.7 versions, in drivers/net/usb

Remove references to __devinit and __devexit and __devinitdata from all bcm2835……c source files in sound/arm.

This should result in a Pi kernel that will (cross) compile successfully, but not without several ‘warnings’..

Result:
Fedora release 18 (Spherical Cow)
Kernel 3.8.0-pi on an armv6l (ttyAMA0)
………….
# uname -a
Linux rgpi 3.8.0-pi #1 Fri Feb 22 16:13:35 GMT 2013 armv6l armv6l armv6l GNU/Linux

Note:  This should only be attempted if you have some idea what you are doing.   It is a nasty hack, and may well produce unforeseen errors.    Not recommended for production environments, and where data is valuable!

Robert Gadsdon.   February 22nd, 2013.
Updated February 27th, to provide correct link to the 3.7.0-1 patch, as pointed out by Joerg Neikes..