Pro Just works out of the box
Lots of support for hardware, lots of pre-installed software, and a smooth install process means less time downloading drivers, less time digging through configuration files, and less time deciding on software to use just to get up and running. It also means less time digging through forums looking for support.
Con Relatively high system requirements
The default Unity desktop environment is a resource hog which requires hardware accelerated graphics rendering in order to run smoothly, making out of the box Ubuntu unsuitable for low end systems and older hardware. Even mildly aged hardware, you'll get far better performance out of a lighter desktop environment like LXDE or XFCE.