This looks nice and seems to be a decent solution to setting a consistent vertical rhythm, but doesn't seem to really use any Sass features, and the old OOCSS-style layout helpers leave a bad taste in my mouth. Seems easier to extend placeholders rather than use those classes all over the place in your markup. Sure, you CAN do something like this:
<div class="h2 left p2 mr2 bold white bg-blue rounded">.oh</div>
but do you really want to?