Depends on where you go hardware installed. If it is not a core2duo with 2GB minimum RAM is not worth the change, because there will be fine.
Pros:
He's new. If you want to continue knowing using a PC required, since it is what Microsoft is doing usability (look at the office since 2007)
The OS-level user that there is a safer day today.
She has everything good about Windows 7, but much better. Now you can make it boot directly to the desktop, and a future update will start menu.
-Once you learn to use it, you will know use any "pileup" of microsoft Windows or OS (W8, WP8, Xbox)
Cons:
'It's a Windows that does not look like Windows.
-We must learn to use it, but once you learn, is much better, more comfortable and productive. (the charms are indispensable)
-The organization of installed applications is very intuitive, especially if you have a lot installed.
There is plenty of software for Windows 8/8.1 looks like Windows 7 in all aspects, although personally I recommend that if you have Windows 8, Windows 8 uses as it is.
Almost everything is my personal opinion.