In July, the Strange Horizons fiction department received 488 valid submissions, making July the 7th-highest-volume month ever. (And only a few submissions short of being the 5th-highest.) That's an average of nearly 16 stories a day, down a bit from the unusually high volume in late June, but up by a full story-per-day from April's average.
The last two weeks in July made the top-15 highest-volume weeks list, with 124 subs in one week and 120 the next.
Comparison to recent years: July of 2008 saw 568 subs (over 18/day), but that was after a two-month closure. July of 2007 got only 363 subs (a bit under 12/day). So one way of looking at this is that submission volume (in the absence of unusual circumstances like temporary closures) has gone up by over 30% over the past two years.