Late last week, we were amazed to see Speck announcing a limited-run collaboration with beer-maker Guinness on a Speck x Guinness St. Patrick's Day iPhone 4 Case; this week, there's another collaboration: the Speck x Burton Fitted Cases for iPhone 4 ($40) and iPad ($60). Though the basic concept of the hard plastic shell/fabric-backed Fitted Case remains the same from Speck's prior iPhone 4 and iPad Fitted Cases, some new details really caught…
