"Ubuntu" kernel version - what does it mean? I have a 4.0.3 tablet (Genesis GT 1230 running some preinstalled rooted custom rom from factory). It reports its kernel as "3.0.8+ root@ubuntu #412". 

Why "ubuntu"? What does it mean? Do I have Ubuntu on my Android tablet? Is it any different from an ordinary Android?
The string "3.0.8+ root@ubuntu #412" is the Kernel version of your Android. It doesn't mean your device is running Ubuntu, though: It's not unusual that the kernel version includes the name of the machine it was compiled on. So it just tells you what the dev of your custom ROM uses for development.