I routinely find this expression in newspaper, magazines, blogs... My guess is that it's used to report a widely shared opinion, but I couldn't find any confirmation of this. Or maybe it's just used to emphasize the adjective? I'm afraid I might be missing a subtelty here.
Here are a few examples from the first page of googling "oh so *":
- Paul Ryan's oh-so-clever jab at Jay Cutler
- Chivas USA came oh so close to getting the first goal of the match
- The movie-star-handsome [...] stung with that oh-so-direct comeuppance
- Robert Pattinson Oh So Lonely: 'No One Ever Calls Or Texts Me!'
- An Oh-So-British Affair Projects a Fresh, Antique Charm
- LaPorta made an oh-so-costly error in the game
- Finally, the long, oh so very long flight back to Vancouver