One of the biggest pains of developing for the web is the necessity of having to make sure all of your sites work in Internet Explorer 6, which came out in 2001 and yet is still used by 20% of users (October 2008). IE6 sucks at handling CSS floats and positioning. Most of the issues are resolved by using a Global Reset Stylesheet but I still find myself occasionally running into new problems for IE6, like with the Suckerfish CSS dropdown menu first created in 2003 at http://www.alistapart.com/articles/dropdowns.
Then came Sons of Suckerfish which still didn’t do the job until I came across Sons of Ursidae (http://css-class.com/articles/ursidae/) which has done the job, at least for now.
Gotta run, this post was more of a mental note to myself, sorry!