If one got good feedback from a double-blind review, is it ever possible/ justifiable to find out who the reviewer was? I got some impressively lengthy, detailed and mostly positive feedback in a double-blind peer review for a paper. Is it ok (or even possible), or is it against best practices (and considered taboo), to try to find out who the reviewer was - just in case you can get more feedback and share ideas related to the topic at hand?
As @SE318 explains (+1), it is unethical to try and find out who a reviewer is.  However it is not unethical for a reviewer to identify themselves if the so choose (some journals specifically give this option in their review form).  I can't see much problem with sending the journal a polite request for the editor to pass on a message explaining what you had in mind so that if the reviewer was interested in collaborating they could contact you.