My hunch was right. There is an unannounced cut-off for free downloading, because Rapidshare is working again for me. It's about 24 hours after it stopped working. No idea what the actual amount limit is, but I'm guessing it's somewhere in the 1 (maybe more) GB per day range, then they cut you off for 24 hours.
Anyway, suffice it to say, I'm relieved.
Fango