Check out these pictures of the Surly Pugsley:
http://www.surlybikes.com/surlyblog.html (Sept. 28 & 30 entries).
Interesting comments, at least to me, on why it looks as it does:
"In order to get that much tire clearance, we had to use a 100mm wide
bottom bracket shell. But since this created poor chainlines issues, we
offset the rear hub 17.5mm to match up the front and rear chainlines.
The other thing odd about this bike is the matching 135mm spaced offset
fork. This allows you to interchange front and rear wheels for gear
changes on singlespeeds or if your freewheel/freehub froze up. We are
going to make 17.5mm offset adapters for wheelbuilding ease as well."