Tim Ireland says:
A slow day at Bloggerheads amounts to about 1,200 individual visitors (to the main blog, i.e. not counting any of the other pages on the site)
A normal day runs at around 1,700-2,500
Busy days go to 3,500 and up.
PS - Make sure your submitters don't get page views (eg views of individual posts) or hits (ie no. of files downloaded) mixed up with unique visitors to the main weblog.
The figures I've provided here do not take views of individual posts into account (such as the 11k peeps who have read my Crazy Frog post, but have gone no further).
If I took these visitors into account, the figures would start at 3,500 per day and then go up on busy days.