A few days ago I finally got to the next thing on my Want to do this year list: put a new android (Cyanogenmod) on my tablet, which was still running the stock Android - but hasn't seen any updates in more than a year. Considering the (in)security of Android this was long overdue for me. But the fear of getting an unbootable tablet ("bricked" as it is often called) was keeping me from doing so.
So when I finally got the nerves, I first had to run around screaming for hours because the first step in the instructions didn't work. The next day I read that it might have to do with the cable - and indeed, tried with a different cable and the instructions just went along just fine. So today I'm happily running with a more up-to-date Android again on my tablet.
Because my systems run Gentoo Hardened with SELinux, I did had to do
some small magic tricks to get the
Clockworkmod recovery on the tablet: the
wheelie binary (yes, I couldn't find the sources - if they are even
available) that I had to run required me to disable size overflow
detection in the kernel (a PaX countermeasure), allowed executable
memory (both through paxctl-ng as well as in SELinux using the
allow_execmem boolean) and had to temporarily add in the
dev_rw_generic_usb_dev right (refpolicy macro) to my user.
Also adb had to be pax-marked, although I now know I don't need adb at all - I can just download the latest Android ZIP file from the phone itself and refer to it from the recovery manager.
All in all nothing to worry about - everything worked like a charm.
Edit: (so I remember next time), if the system is stuck in CMR (recovery), reboot with VolDown+Pwr, but don't select recovery. After 5 seconds, it will ask if you want a cold boot. Select it, and things work again ;-)