I recieved this email in an account that isn't registered with paypal. I clicked on the link and it goes to paypalsecurecenter.com, not a link on the regular paypal site. I just thought I'd post it as a warning since it actually looks pretty official. Sorry if this is old news, but I hadn't seen it before.
ETA: Sorry, I tried to copy the email but it didn't work (although it was fine when I previewed). Anyway, the email says that your billing information is outdated and you need to click on the link to update it. The link takes you to a site that looks identical to the paypal page but the url is different. Sorry I couldn't copy the message.