Just spent the better part of five hours cleaning up four old, out-of-date Wordpress installations after they got infected with this worm. I host nine sites on my home server for friends and family; I'm cutting that down to three (just family), and maybe looking at mu-wordpress, as of Real Soon Now.
Happy Labour Day, everyone!
Update: I meant to add in here a few things I looked for, because this info was hard to track down.
I found extra admin-level users in the wp_users table; some had their email address set to "www@www.com", some had random made-up or possibly real addresses, and some had the same email address as already-existing users.
On one blog (possibly infected much earlier) I found 42,000 (!!) approved, spammy comments.
I searched for infected posts using a query from here:
SELECT * FROM wp_posts WHERE post_content LIKE '%iframe%'
UNION
SELECT * FROM wp_posts WHERE post_content LIKE '%noscript%'
UNION
SELECT * FROM wp_posts WHERE post_content LIKE '%display:%'