is apparently
Not A Nice Thing.
Rumor has it that it steals LJ passwords, and possibly contrives to hijack your LJ account. And the HTML code it generates does nasty things to at least some Mac browsers - kind of like what happens when someone posts a really wide picture without using a cut tag.
This public service announement is grabbed from
pewtergryphon, her source is
linaelyn, the latter has a writeup at
http://www.livejournal.com/users/linaelyn/627662.html