I installed the latest Xcode and Yosemite betas several days ago and have noticed a feature of Yosemite seems to be its not possible (by design or bug?) to click on a a scroll bar and drag.
This was an irritation but now I'm trying to navigate within a storyboard and there's no apparent way of moving around - there's no navigation bars, there's no arrows, pressing arrows on a MacBook keyboard does nothing, its not possible to click within the story board and move it around, there's no zoom/de-zoom button to expand/collape the Storyboard.
I've been scratching my head then getting increasingly irritated, I just can't see any way of repositioning a storyboard with Xcode and thus I can't do a thing at the moment - there are view controllers in my Storyboard not displayed on screen and I just can't get to them!
Moving around the Storyboard works the same way that it has always worked: drag with two fingers on the trackpad or click and drag the scroll bars.
If neither of those are working for you, it's a bug and you need to report it. Also consider reinstalling Yosemite and/or Xcode because I am unable to reproduce this issue.