I often wonder that as well, we seem not to get anywere that figure. It was though at the height of all the flooding we got in the summer of 2007, so maybe FWH remarks might have some truth. I also look at users in a 24 hour period which was 1088 we nearly reached the other day, but it does puzzle me that you would thought that if 665 users we once logged on in June 2007 then you would asume that daay would also have the most users in a 24 hour period.
It was Yahoo's search engine spider which went a bit mad and it was spidering with several hundred computers all at once.
It was a temporary glitch, and many people complained (because it could bring a small server to its knees) and Yahoo fixed it soon afterwards - though occasionally they still get it wrong on some sites.
The highest number of users only looks at logged in users (and I only did that recently, so it doesn't go back that far). Spiders and guests are not considered. The 1088 day was one where I sent a mass PM about filling in a survey.