Originally Posted by Plan9
I've not ran it myself, but from what I've read in the past, I believe only the BSD kernel reside in GNU/kFreeBSD. A lazy Wikipedia
search would confirm this too - if you're happy to trust such a source:
Didn't use it for long, it has a few issues, but that is about the gist of it, the BSD kernel, with GNU Userland, combined with the immense Debian package base.
you can find out more info in its debian wiki, gives a bit more info about what it is, what its made of and why it was made than the wikipedia page gives.
I really didn't care much for it, it was a bit unstable, and like freebsd not all my hardware works correctly with it (it might now).
I would agree wtih tompsonn and plan9 on the differences they've already mentioned, and would add my own Linux is open sourced, i can look at the code to see what makes a kernel tick, and NT, i can not :) (even tho i'm not even remotely interested in kernel development).
and @plan9, thats an old old (like 9.04/9.10) image of the software center:
the latest version in 12.04 is very polished compared to the days of old :)
but yeah, you use this mainly to install software in ubuntu, either from the repository or from a deb in the wild. there are other gui's, but they no longer come bundled in a default ubuntu, and there is really no need for them, and yes, you can always revert to the command line and use apt or aptitude (which you will have to install using apt or the software center in the later editions of ubuntu). My favorite feature of the software center is the software sync feature, where if i install something on my desktop, and i want my laptop to have the same software i just log into my ubuntu one login account, and sync my desktop to my laptop. there are other nifty features they've been introducing, a bit iffy on the few, like landscape.
as for root privileges, in ubuntu and most distro's, the first created user account is generally added to the group that can use sudo, to elevate their privileges to do root only things, but in ubuntu, unlike other distro's, ubuntu randomizes the root account itself password, so you don't set it up during installation, and the only way to change it is to use your sudo privileges in the main user account, and switch to root and then change it.