Pros
Sometimes they have free lunch on the weekends. It almost makes up for the gas you had to spend to come work for free. Most of the people that work there are actually very nice and smart people, enjoyable to work with.
Cons
You will be pressured into working almost every weekend. You're family will miss you. You will have no work / life balance, work will be your life. The culture is very subservant to management and having to donate nights and weekends does not seem to bother many of them in the least. Having to work the weekends is mostly a product of bad I&T support and lack of availablity of equipment to work with. There is a huge resource problem here that involves lack of products to test on, lack of computers to work on, lack of network bandwidth, lack of cables and even lack of restroom bandwidth! So they could buy more equipment (which costs money) or they can have you work the weekend (which is free).