The ads-l has had a nice thread today about Michelle Obama's (really good, IMHO) speech last night, with reference to her retroflexion of /s/ in str- clusters, so that words like strong, street, string start with more or less a [ʃ] or 'sh' rather than an 's' sound.
This piece of American English usage has been the topic of some very nice sociolinguistic work (David Durian's research on the Columbus area was noted over at ADS, but there's other stuff too). Last night, I noticed this feature immediately but what really struck (shtruck?) me was that she was doing it every time, in word-initial and word-medial position. I haven't gone back and tracked the whole speech, but I'm used to this as a highly variable pattern, while it seemed consistent for her.
This also seems to be one of those innovative features that isn't being condemned, at least not that I've heard.
Maybe it's just one more way that she's progressive!