During the month of January, 2008, Strange Horizons received 494 valid submissions--our highest-volume month ever, but only barely edging out January of 2007, when we received 492 subs.
Certainly volume was significantly higher this past month than it usually is; we've usually been averaging about 350 subs in a normal month. But January volume was much lower than I was expecting; I was originally guessing it would hit 700, then later downgraded that estimate to about 600, and I was pretty sure it was going to be at least 550.
I forget whether I've mentioned my current theory about all this: I'm thinking that if a writer shows up to submit and finds SH closed to subs, if the reopening date is less than two weeks away, many writers will wait and come back in a couple of weeks and submit after we reopen; whereas if the reopening date is over a month away, most writers will go submit their stories elsewhere. Thus, closing for two months (as we did this past November and December) doesn't result in significantly higher volume on reopening than closing for one month (as we've done in December in the past).
I have no idea whether that theory is true, but it would more or less fit the data we have available.
The good news for us editors is that if this year's numbers continue to mirror last year's, then February will be substantially lower volume.