Originally Posted by fatbat
Not talking about front versus back racks. I've seen some euro bikes where the rack is in the front, suported by an extension from the top/down tubes, not the front wheel. This gives you the advantages of the front rack, without having to actually wrestle all that weight around whenever you move the front wheel.
The royal mail bikes here do that.
http://static.flickr.com/8/8109852_40332b24db_m.jpg
http://genetics.mgh.harvard.edu/hanczyc/jpg/market2.jpg
They are very easy to steer at low speed even when fully loaded. It might be a bit easier in really tight spots if the rack rotated with the forks. When doing tight turns with a fixed position rack the wheel is turned sideways but the rack is still jutting out forwards, effectively adds a couple of feet to the wheel base.
If you spend most of the time without a load fixing the rack to the fork makes sense.