Looking at your books ranking in Amazon can be a mildly obsessive pastime, like checking your Technorati rating (465,937 since you ask). In Amazon yesterday I had risen to the giddy heights of 9,432. To put that in context Harry Potter and the Half Blood Prince is 97, Moby Dick is 1,428 and Perec's Life A User Manual is 639,483.
But before I could purchase the yacht, it seems my fantasies of retirement were scuppered by the long tail. Sales fall off very quickly after the first 1000 or so, as this article explains. So at around 10,000 it is selling 11 copies every 5 days. It'd have to be a pretty small yacht under those circumstances. And this seems to have been a peak (probably a couple of friends bought a copy out of pity), as today I am at 63,108. Of course it would be a very sad person indeed who looked up how the books of their colleagues were doing, so you won't catch me doing that, oh no.
(Thanks to Chris Pegler for the link).