I just found out about Duotrope's Digest, a site that's a combined market list and submission tracking system. (It's been around for at least a year, so many of y'all probably already know about it, but I figured it was worth mentioning anyway.) It joins the ranks of such other nifty online market lists/databases as Ralan's Webstravaganza, StoryPilot, and Quintamid (though Quintamid seems to be unavailable at the moment), but it has a pretty nice interface and a pretty extensive list, and collects a whole lot of stats (especially regarding submissions). Sure, you can always check the Submitting to the Black Hole page to get response time data, but that won't tell you the average submission-acknowledgment time....
Duotrope also provides some other stats, such as a summary of visitor searches (87% of their searchers are looking for short fiction publications; 88% are looking for print publications; 94% are looking for markets that accept electronic subs); a list of the most-visited listings; and publications ranked by response time (where Lone Star Stories ranks first, with an average reported response time of 0.25 days).
You can also view a calendar of upcoming themed venues, and you can sign up for a free weekly newsletter listing new and updated markets, etc.
The main problem that I see with their system is the relatively low quantity of data (their acceptance-rate stats are a little skewed by this). So I encourage y'all to report response times there. If you register with them (for free), they'll track submissions for you, but you don't have to register to report a response time.
Anyway, stop by and take a look!