success rate? i have no idea. i've had a lot of issues with copyright in the last couple of weeks. the first involved my blog and after contacting the copier's hoster, they gave me a pile of instructions of all the forms i have to fill out, which must then be sent registered mail to them and they will look into it apparently. hoster's aren't that interested (despite their 'agreement' that cites a user won't violate copyright) b/c it means lost money for them if they take down a blog (i.e. no renewal). for now, it's wait and see although the copy was verbatim.
worse yet, I then found out from an employer that a medical journalist (really, that title should be quoted..-bitter laugh-) had stolen around 150 articles verbatim that I had written for my employer. my employer owns the copyright to it so in a sense, it's their mess to deal with but it was shocking how well published this person was and how much he'd stolen of stuff I had written across so many therapeutic areas. you somehow just don't expect someone in that position to steal, and so blatantly...more shocking is the places he has been published-i'm shocked they don't use copyscape.
i'm sorry to hear that you've been plagiarized and the unfortunate reality is that today, it's not a case of IF you'll get copied, but WHEN. you have to decide what the stress level is with a specific instance of copying and whether the time/energy is worth it. I seriously wish you all the best. :)