Here are some points about the stats:
1) we have a bunch of statistical data, but the graphs you see were not prepared by someone with statistics skills (that would be me). Syskoll has broken out the graphs on the popup page, to make them more clear -- I think we could still make things a lot better if we thought about it for awhile.
2) the graph on the front page will often appear to be decreasing, and the bar for today is "real time", so it'll almost always appear less than the previous days (except for at 23:59 PST) -- spam is always higher in the first part of the work week, so you'll see a decreasing trend if you look at the front page graph on the weekend.
3) the popup graphs do show a marked decrease in the last couple of weeks, but if you look at the last 6 months (or longer, if you could), you see a roughly cyclical rising and falling pattern with a general upward trend. The recent decline still fits that pattern (if it continues for another couple of weeks, it will break the pattern).
I'm starting to think about analyzing the stats to see if we can determine any effect that the U.S. CAN-SPAM act might be having. There is no obvious effect based on the graphs we have now
If you or anyone you know (or anyone who reads this) has some ideas for interesting graphs, we're "all ears" -- one thing to note, we only keep track of the date for events, not the time-of-day. Time -of-day stats would be great, but it's just too expensive to maintain the data.