Having gone through this, I see some valid points in most of the posts, although I'll try to add something instead of being the "I agree with everyone" guy
I went to college 50mins from home and commuted. I hadn't planned on staying on my team (despite loving it so much) due to both schedule and wondering if there was a place for a college student, kind of echoing some of Ken's concerns way back in the thread. However, my team approached me in 2006 (my freshman year at UNH) and asked me to come back and help them with the vision system, since I had jumped in over my head with that on the Tetra year trying to get Labview to run on a PC on the robot. Yeah, that was legal before we made it not :-)
I have been a mentor ever since, and now I'm a finishing grad student with five years in heavy construction. Its been very hard to find the time, but for me, it was worth it. You do have to prioritize and there are places I wish I had spent more time on my grades than on FIRST. And if you think that is hard, try getting married
Being a newlywed college student new job mentor is pretty tough! But prioritizing, time management, and being intelligent with your resources really helps you get the most out of all of it.
I do want to strongly encourage anyone who is in college and thinks they can handle it to DO IT. The more time I spend in the "real world", the more I realize that the FIRST experience and mentality is desperately needed in the professional world. The "real world" is plagued by a lack of vision, a crippling fear of failure, and the ever-present "box" that most people can't seem to cut their way out of with a torch. It sinks innovation and is the reason we are falling behind. Other countries don't have some of those issues with their engineers and builders, and they're leaving us in the dust.
FIRST forces you to work with people of very different skill levels, and for a college student that involves both engineers who know way more than you and students who know way less. You want to build character? Try mentoring in that environment. You will learn pretty quickly that humility, initiative, and care for people is alot harder than you think, and its lacking in our workplaces. Being a mentor in college has benefited me far more than being a FIRST student, and is the reason I am (admittedly) doing very well professionally and regarded as a can-do problem solver willing to tackle and learn anything. Those are things I learned through hard work in FIRST, and has changed me as an engineer. That little mental hurdle at trying new things that you have to get over as a student will come in real handy when you're on a steel beam over a river, there's a technical problem, and its time to cowboy up and get the job done! Engineering can be exhilarating, and I learned that through FIRST.
Long story short, be responsible, but be a mentor! You won't regret it! Even if you fail, you'll learn something!