Lots of bitter people in this thread. Hmm. Some thoughts from someone who doesn't regret it:
1) After college, you lose a lot of advantages you had in college. In college, you had facilities access, a coach, a team, a racing season all planned out for you, a relatively free schedule, etc. After college, you need to leverage the advantages you DO have to get the most out of your running.
As a post-collegiate, you have the advantage of being able to have a completely personalized training schedule. You don't have to race when you're not ready. You can do true six-month training cycles without a bunch of useless indoor track meets in January. You aren't even stuck with a traditional 7 day cycle. Beyond this, you need to find out what particulars about YOUR situation you can take advantage of. Can you run during lunch? Can you eat breakfast or lunch at your desk at work? Is there a nice bike path you can use for tempo work? Can you get on a track? Do you have a gym at work? Etc etc. If you think hard enough there's probably some advantage you can use.
2) Get a coach unless you really know what you're doing. Which you probably don't.
3) Do the stuff you didn't do in college. Lift, do strength exercises, do more fast runs (or slow easy runs), whatever. That is where you'll see a lot of improvement. If you keep doing what you did in college, you'll get the same results. You should substantially change your training. Join a gym, it's great to have a place to do all that strength stuff you really should be doing. Also nice to have a pool or bike if you get hurt.
4)Try a new distance during your first year or two out of college; it's very hard to do well at the distances you focused on in college the first year of post collegiate running. HM and Marathon are natural choices, but the mile can be fun too if you were a 5/10 guy in college.
5) Give back to the sport and/or your community. Running is a lot more fun when you share it with other people. Focusing only on your own running is pretty selfish. Volunteer coach at a high school, or help out at road races, or a kids running club on the weekend, something like that. Giving back to your sport and to your local running community will do wonders for your enjoyment and appreciation of the sport. It will also help you when things aren't going well in your own training. Do this even to the detriment of your own training.
6) Don't train harder than you can sleep. If you're not gonna get enough sleep, trying to run huge mileage is silly. Figure out how to be more efficient with your time first. A lot of people who complain about how busy they are just aren't good at time management. Eat at work, pre-cook meals on the weekend, etc. If running is important to you, figure it out.
7) Have some fun, geez. It's okay to grab a few beers with your friends on Friday. You'll run better when you have balance in your life.