Yeah, I basically blew off college for the middle 6 semesters, barely graduated, flunked two courses in my major, was on academic probation twice, and skipped probably well over half my classes, and have no regrets. It was nice to stand up on the stage and get my diploma - a year late, though I didn't need to take any additional classes beyond my 4 years - and remember that I got
everything I wanted out of college.
I actually didn't spend much time drinking and doing drugs - my reasoning was that I actually wanted to remember college. But I got involved in a bunch of clubs & activities, just hung out and chilled with my housemates a lot at like 4 AM, got to know hundreds of friends through the Internet, studied abroad, learned Lisp and functional programming, took on a major software rewrite for a popular website, went to a few parties (enough so I felt like I didn't miss out anything), had lots of quasi-intellectual discussions with friends, read lots of books, visited local attractions, and took courses at other colleges in the area. I feel like this is an opportunity cost that I'd regret missing a lot more than the class-time and homework assignments than I skipped.
The irony is that it doesn't seem to have harmed my career at all. Once you get that first job and do well at it, nobody cares how you did in college. And I got that first job through a friend I'd met on a programming website on the Internet, while I should've been doing my homework. Score one for slacking!