http://cgi3.ebay.com/ws/eBayISAPI.dll?AboutMeLogin
Now go to :
http://members.ebay.com/ws/eBayISAPI.dll?EditUserPageHTMLSourceand edit with HTML enabled.
Demo URL (My profile):
http://members.ebay.com/ws/eBayISAPI.dll?ViewUserPage&userid=shell2h4ck
It is also vulnerable to redirection and other normal xss attacks
One of the possible exploitation scenarios is malicious people stealing cleartext credentials from registered users by injecting an iframe tag that retrieves another rogue eBay login page from a remote server.
http://xssed.com/news/125/Persistent_XSS_bug_discovered_on_eBay/