They normally only stay good a couple weeks, but with some effort, but you can keep them green and fresh until well into the new year. The stand I have this one in keeps the tree upright, and also holds water for the tree to drink. It takes at least a few cups of water every day.
I think there are pros and cons to real/fake trees, sometimes a real tree isn't suitable, or there isn't a good supply nearby, or you don't want to water it, etc : P