Not wanting to sound like a nerdy geek type but...life as a postgrad student is very different to undergrad life. You have to work a lot harder and hence, have less time for socialising. Also, a lot of postgrad students have not come straight from an undergrad degree (maybe worked or travelled first) and are perhaps older and have more responsibilities out of work. However, I'm sure you'll meet some like-minded party people and have fun, as the PhD team said, life's what you make it! :o)