our team has never really had a problem with numbers of people so far as i know, except for the animation team. i am a junior, and last year was my rookie year. last year i was the only one on the animation "team" and i spent all of my time playing around with 3DSMax. i never actually submitted anything because my laptop, which was running windows ME (bad bad bad bad bad bad bad idea

) crashed. so this year there's at least three of us. i think the main reason that so many people left our team was because everyone came in (mostly freshmen) assuming they would be driving the robot. when they found out that there would be only 2 or 3 drivers, a handful of them quit. i suppose they were just looking for some fun without working for it. of course, the 12 people and 2 human players who want to be part of our drive team have been informed that there are four practices a week, involving setting up and tearing down the playing field every time. i suppose this was a turn-off enough to those people who just wanted a free ride. to tell youi the truth, our teacher was mad at the fact that we had 40 people at our first meeting. but freshmen will be freshmen and now we have around 30 or so, which cis good because all areas of our production have had an increase in members from last year (especially animation---yay!

)
i think that if teams are having trouble with a lack of retention, they should be telling members even before they come to the meetings, how much work is involved. i think that videos of the team competing from the previous year (s) are a good way of showing members that, despite the work that they know they will have to be doing, it actually does result in some fun and friendly competition, even if you're not the driver. i know i've screamed myself hoarse at several competitions.....
good luck with recruiting next year, since it's kinda too late this year. but know that if people quit, it's no use trying to bring them back as they will only be counter-productive.