Ah, OK. Yeah, a twist in the frame would be a tougher problem than the simple cupping I was envisioning. Now I do remember someone talking about how their printer wouldn't sit flat, so they might have had a similar problem. Unfortunately I don't remember if the problem was resolved. Could have been discussed in the MakerFarm IRC channel and not a thread...

Haven't noticed any issues in my printer, but I did glue it up as I built it, checking things with a square and clamping joints where necessary.