?nohtml=1to the URL of whatever friends page or journal page you're viewing, and it will escape all the HTML in the entries. (An example would be http://www.livejournal.com/users/lj_nifty/friends?nohtml=1. This can also be used on customview links, such as http://www.livejournal.com/customview.cgi?styleid=9488&user=lj_nifty&nohtml=1).
This lets you see the code they've used in the posts, but it doesn't have any effect on the page. Very useful if someone posts a gigantic image that stretches your friends page or takes ages to download, or if someone in a community forgets to close off a <marquee> tag and the whole page starts scrolling :)