Manchester's a great place to be: it's small enough to travel around easily and yet it's still packed with all the shops, restaurants, theatres, galleries and museums that you'd expect to find in any major metropolitan city. It's also a bloody friendly place to be, try chatting to a stranger if you don't believe me.
If you've not from around these parts, you may find these links useful for finding getting around and finding things to do. I hope you enjoy your stay.