[Jasmine Zhou]

We don't use attendance to measure the quantity of people's work so much as their willingness and ability to commit. If, for your team, hours put in is correlated with quantity of work (in some units), then perhaps you can trust the work to someone who doesn't have all the other responsibilities of team leadership, and perhaps you don't need to keep track of things on an hourly basis. I'd imagine that there's probably not a justifiable difference between someone who put in 125 hours during build season and someone who put in 127 hours during build season anyways, since that could easily be the result of rounding over several weeks.
For each of the past two years we have designated someone (who is given the unofficial title of secretary and a couple of other responsibilities) to take attendance, making note of latecomers. Both years it started out as calling out names and by about a month in turned into the secretary checking people in by sight. We have a spreadsheet with names, dates, and people being present, absent, or tardy (1, 0, T to easily add sums when we're making decisions). Because meetings have an expected duration, and school day meetings are about half those of weekend ones for us, we can weight the meetings accordingly. A similar spreadsheet is (or should be) maintained for our regular fundraising efforts.
This doesn't preclude people leaving early or five minutes into the meeting, but we haven't had problems with that so far since people have usually been too lazy to game the system, and there are the occasional end-of-meeting check-ins to catch that.

(P.S. sanddrag, that's an awesome system. Once I'm on a computer that actually has Excel, I'm going to play with it some more and see if our next year's secretaries would like to use a similar system.)