During my time there (late 2000s) there was a Software Lab (6.170) that focused on programming fundamentals and culminated in a four-person, month-or-so long project. At least at the time, it was one of the more notorious courses in terms of time investment. It was common for people to live like monks during project time.
Unfortunately I heard that class was retired and there was no direct replacement, which is a shame. It was an excellent crash course in shipping.
when i took 6.170 it was CLU. it was 15 units because of lab, but yeah, time sink.
Project courses were pretty notorious. I had a few. 2.70 (which I think is a different number now) in mechanical engineering was a HUGE time sink. [For others: was a design challenge competition with a live context.] Did another all-terrain vehicle competition in grad school which was probably an even bigger time sink.