Myself, I wouldn't say completely unusable. I do about half my reading (and sometimes replying) on my smartphone. It's clunky and the text size is sometimes inconsistent, but I manage.
Any internet browsing on a smartphone is going to be different from a desktop. I don't blame the forum for that, I blame the smartphone. That's 'smart' phones for you.
That said, I know what you mean because I've seen some forums through my smartphone that are easier to read, if only for text size.
So MetroMPG and Daox, is it possible to format Mirageforum.com for mobile use?