I've checked how the pages look on the phone and on the *pad tablet (the latter only using Chromium's "simulator").
On tablet it looks pretty fine, I'd say, especially when using landscape orientation.
On phones situation is rather clear: some pages look quite OK on landscape mode but generally pages do not look nice. When someone is really motived she'd manage to read all the content (ie. I'd consider that the page is sort of usable). I doubt there is much we could do about improving this without using media queries and introducing some "real" responsiveness.
It looks to me that there is a clear choice: Either we have multiple-column-like layout with quite some content in all columns, or we have all content displaying beautifully on the phone-sized view ports (that excludes multiple columns in my opinion).
I am moving this ticket to the review column. Please add here some comments, opinions, bug reports etc. on particular things not working on mobile (with focus on tablet-sized view, I'd say).