As HappyGuy said, Ubuntu is really easy to set up. It's also more cutting-edge (if you use the latest version) than some other distributions, but usually more stable. There are other distributions that you could use which are more cutting-edge than Ubuntu, but aren't as easy to set up or are less stable, then there are distributions which are more stable than Ubuntu but less cutting edge (and may or may not be easier to set up).

I think Ubuntu is a good middle-ground distribution, that most people could easily learn; although I'm not sure I agree with every direction it is going.

I won't discuss it's merits or faults in relation to other distributions; I'd rather not start a fight, and I'm really not the best person to discuss those points with, anyway. Suffice to say, you should try different distributions yourself (in a virtual machine, if possible; although it may not perform as well as if you had installed it to disk) and see which ones you like. I'd spend a minimum of about a week getting to know one distribution. After that, you can try others and probably determine whether you like them or not in about two or three days (although longer is better).

Can't say whether Windows 7 is better or worse than Ubuntu; Haven't used it. It seems like an okay operating system, though.

Re: "terminal stuff"... GUIMiner works on Ubuntu, IIRC.

(I use fedora, btw)