A poster over at Slashdot claims that he spoke with the Mac mini team leader, who said that the Mac mini has had the best ever launch for a Macintosh computer.
Although I cannot vouch for the authenticity of this post, it does make sense. The Mac mini has received the most interest I have ever observed for a Mac product, not just from Mac fans, but from everyone else too. Furthermore, The Mac mini is not only outselling all other computers currently sold by Apple, it is even outselling the iPod at the Apple Store. And while Apple had stock on hand immediately after the Macworld Mac mini launch and was able to deliver units out to customers within days, demand has far outstripped supply and there is now a 3 week backlog. Target has removed the mac mini from its website, stating that they're sold out and have no idea when they'll be able to get stock back in. And the current number one selling desktop computer at Amazon is... you guessed it... also the Mac mini.
The Mac mini is an unmitigated hit. The DigiTimes claims that Apple has contracted Foxconn to produce over 100000 Mac minis per month, but I suspect that will be well over that number.
By the way, that same Slashdot post includes an interesting story from the Mac mini team leader about how the size of the mini was chosen. Apparently the engineers were asked how small they could make the mini. When they came up with their smallest possible size, they were told to make it one size smaller. :)