Driven dotty by Internet Explorer
One of the reasons for using the 2-pixel dotted lines for many of the borders on this site is Internet Explorer's non-existent support for a 1-pixel dotted line - it actually renders out a 1-pixel dashed line instead.
There is, however, an interesting hack that attempts to make up for this deficiency that's been put together by Kalsey Consulting that in itself makes use of the quirky star HTML bug present in IE.
Overall, it's a useful technique to get around one of IE's many bugs, quirks and oddities, but not one I'll be pulling out for everyday use just yet.