has anyone seen this on their sites? is this something targeted specifically at Drupal?
This is definitely not targeted at Drupal, so nothing to worry about. I've seen tons of weird stuff in my logs, usually they are either spammers (trying to put their URL inside my referrer stats which might be spidered by search engines) or viruses/exploits trying to exploit Microsoft IIS. There are no known Drupal exploits, though we did fix a Javascript/XSS validation error in our last release (see the 4.5.2 announcement).
Steven Wittens