I always had a policy of not socializing with people from any company I worked for, but many folks love spending their time with fellow employees outside of the office.
I find it a dangerous move, especially if there will be alcohol involved. The possibility that behaviors observed while relaxed, can work against you when office politics come into play, IMHO.
Have you spent time socializing with fellow employees? If so, how did you weigh the benefits of camaraderie with the risks to your carefully crafted office image?