I have!
The culprit -- whose copyright agent [edit]appears not to[/edit] respond to DMCA takedown notices unless they come on law firm letterhead -- is none other than Amazon.com. (I've caught scumbags selling books of mine online as ebooks via the Kindle store. Amazon don't listen unless you carry a big stick. My solution was to grab the nearest big stick, in this case SFWA's Griefcom process, but something like that's not really an option for most self-published authors.)
(In contrast, Apple -- same situation, only in the iBook store -- were the very model of efficiency and helpfulness.)