I did FLL starting way back in the 2001 season. We won the Director's award in 2002 and 2004, (note that the FLL season + 1=FRC season), and part of winning that was that the team got scholarships for a summer camp for middle schoolers put on by Maine's magnet high school (MSSM). This basically forced me into spending a week up there, and to my surprise I had a great time and even moreso the counselors (who were students) were awesome.
So I ended up spending 3 years of my high school career there, having a great time and doing more work than anyone ever should. Coming from a family of commercial fisherman, hard work isn't really something I was ever opposed to, but working hard at school was just something I never had to do.
Since my home FRC team was so desperate for mentors, I got invited to participate in 7th since they needed my dad. I was on the team full time in 7th, 8th, and 9th grade, and while I was at MSSM our breaks lined up so I still got nearly 4 weeks of build season. MSSM is a state funded school, but we don't need all of the required school days. As part of a deal with the legislature, students spend 2 weeks in "J-term" where you can either stay at the school and take a full time class, or stay at home and find a 2 week internship or job shadow. They are "classes" in a looser sense of the word, as some of them have centered around things like building a
30' tall inflatable penguin. I obviously spent two weeks at home so I could work on the robot, but I also found interesting things to work on during the day including jobshadowing at a local snow plow manufacturing plant, shadowing the local airport manager, and restoring vintage airplanes.
I came to RPI and have been to visit 2791 a couple of times, but honestly I'm involved in clubs on campus already so I haven't done much in college. Last summer I interned doing aerodynamics for commercial jets in Puget Sound (not a huge leap to figure out who for...

), and I'm going back full time when I graduate in a couple months. I plan on getting reinvolved with FIRST at that point.
That particular company won the Founders Award recently, and their commitment to FIRST runs deep. They sponsored one of the first teams, and when I interviewed the hiring manager saw first on my resume and said, "Hey! I did that in 1993!" which made for interesting conversation. I also interviewed internally for a rotation program, and the hiring people there were also were interested in FIRST experience. They also had a huge FIRST tent at
Seafair, which was neat to see.
Long story short, my involvement in FRC and being an Eagle Scout were the two things from high school I had on my resume, and managers tended to be more interested in FRC than the Eagle Scout badge.
Also interacting with people in college, I'd say FIRST alums give you a better shot at being decent group members -- but far from make it a sure thing.
I think FIRST is an exceptional leadership training program, and I'm surprised more companies don't take advantage of that. You basically cram an entire development program into six weeks that takes years in the real world, and it happens every year! Almost all of the problems you get in the real world, you get in FIRST. We like to think of FRC as a great opportunity for students (and it is), but it seems to me it is just a good opportunity for mentors.