You will cause a lotta more problems disconnecting it than leaving the battery connected. As mentioned disconnecting it zero-outs the many computers, radio, alarms etc. Dont leave a trickle charger connected to it either as they usually are cheaply made with cheap surplus parts (read: fire hazard). When you get back, if the car wont start call AAA or connect the trickle charger to it overnight. I often travel for 3 or more weeks and only once was the battery dead after a 6 week trip.
And forget about old wives tales such as draining the oil, putting the car on blocks and removing the tires, adding stuff to the gasoline etc. Just open the windows 1/4" for some circulation and go away happily.
MisterNice