Recent visitors to this site may have noticed an unintended horizontal scrollbar in IE 6. Simon Willison noticed the same problem on his site earlier this year and traced the problem to italics in blockquotes. John Potter points out that any line ending in italicized text within a block that has either relative margins or a specified padding will surface the bug. Removing italics from text within blockquote and cite solved the problem for us. In testing, removing the padding on the parent block also solved the problem.
To sum up, lines ending in italicized text contained within blocks with relative margins or specified padding will expand the width of their parent block in IE 6. It may seem esoteric, but you'll be glad you read about it first if it ever happens to you.