Back in the days of my Canon 5D the lack of OB wasn't missed. Now, I'm not so sure. Manual flash on the K-3 has come in handy, especially for times when I want to trigger an external flash.
For my purposes, the pTTL lag makes it impossible to use for most situations I encounter.
Now that I have the Joe Demb modifier - I can diffuse light with the OB more artfully and softer than using a Fong on a large flash. Also, I can afford to shoot 800 ISO and bounce light off the ceiling (assuming that I'm using a relatively fast lens). Even without the bounce/modifier, if the FF body provides HSS for bright fill situations (ala *istD) - that's a worthwhile consideration for close range work when considering the shutter sync limitation.
Sometimes you encounter an unexpected situation when traveling light. For instance, I didn't anticipate a request for a situation like this one - where creating a lighting balance was absolutely necessary. Using the manual flash ratio worked well: