+1 to Franco.
Drck, I get what you're saying, and you're probably right, people would do a lot better if they took their studies more seriously (or, better still, actually selected degree programs that taught them skills they could use to make money after graduation). However, that's not what this thread is about.
Kenshin, please... take it down a notch, brother.
On university, yeah, sure, life sucked for me in school, mainly my own doing, and I knew it at the time, too. There's not too much for me to miss there. Every girl wanted to be my girlfriend anyway, so it would've been tough doing too much hooking up for me at the time even if I did have it figured out, and I certainly did NOT have it figured out. I still look back occasionally with rose-colored glasses, and then laugh and remind myself how it really was. I still struggled with the odd relapse into depression until about 6 months after college, and after that it was gone, never to return. Looking back, school always felt like a kind of confinement to me... it was like being locked up somewhere.
In building a life after school, it's going to depend on what you want. If you want a large, college-like social circle, you can certainly build this, though you'll probably be doing in bars/clubs, or the rave scene like Radeng suggests. Most people don't maintain large party groups post-university, because these become unwieldy and impractical. I went through a phase in Southern California where I'd try to get as big a going-out group as I could to go out, and I'd routinely be able to get a group of maybe 10 or 12 people to all head out together, but it was tough getting that organized. Fun though. And at times I'd join other established going out groups of 6 to 15 or so people, girls and guys. These would all be people I met at bars, nightclubs, classes I took, or through friends of friends (sometimes friends of guys I met via pickup forums).
Once I felt like I'd caught up on the social experiences I missed in university, I didn't have too much need for going out with big groups anymore, especially as I found out it didn't help me pick up girls at all (I only recall sleeping with a handful of girls off of these big outings, and usually only because there was an after party at someone's house after), and there wasn't much value for me in just hanging out shooting the breeze with people. It was fun to do for a little while, and then I wanted to get back to self-improvement, but the people who like to hang out in big social groups and drink and party, or at least the ones I was hanging with, aren't too hard-up into that. They're living comfortable lives, and that's enough for them. Plus, I really started drinking heavily when I was going out with groups a lot, and that led to a lot of problems for me. By cutting back on my group socializing, I killed all the problematic drinking.
I became more of a lone wolf once I started traveling again. When I was stuck in one place all the time working a 9-to-5, I guess having friends to go out with was an escape from the grind. Nowadays I'll cram most of my interacting with friends into short periods of time when I'm on travel and swing through cities I have friends in, and I'll crash with a guy and spend a few days just non-stop hanging out and chatting and catching up with him, and then I'm off to the next place. I like this better; without the drinking (or without too much), I can have better conversations with guys, and most of the guys I'm friends with these days are all working on cool things in their lives and I always learn a lot when we compare notes.
Chase