I have breasted up loads of times, its common in cowes for instance, where I used to do a lot of sailing and yes, on a sailing boat you go round the front of the mast when going across boats.
When I have done it in narow boats, its usually in Upton upon Severn where I have been 3 abreast and seen yogurt pots 5-6 abreast and they tie directly to the bridge with a bow line.
The main thing when doing it is to make sure you tie directly to the bank or something solid yourself, dont rely solely on anyone elses knots.
*edit*
I did laugh at some woman at the Camp in Grimley on the severn a couple of years ago that didnt want me to breast up with their boat cos it had just been blacked, her hubby heard the convo and went red and asked me to, so i moored up the stern in front of them and only the back half of the boat on the pontoon and threw out the anchor knowing the river was low and all was fine and the couple stayed in theor boat bless em