While I can appreciate Ron's appeal to detailed excavation methods, much of 
what one can and cannot do in urban excavations is entirely situational.  If 
you have lots of time and lots of money, detailed work is, hands down, most 
important.  That is not usually the case, though, and you have to opt to get the 
highest return for the effort.  

We had a situation in Ogden some years ago where we were allowed only a week 
or so to excavate up to 25 privies, ash pits and cultural midden areas in a 
late 19th-early 20th Century residential area.  We put a lot of effort into it, 
but used heavy equipment where we could to expose and dig around the perimeter 
of identified features. We were kicked off of the site before we could finish 
and ended up leaving many privies unexcavated.  They were subsequently 
bulldozed for construction.

While you want to control the context of the data you reteive as much as 
possible, time and money will end up dictating, to some degree, what you can and 
cannot do.

Mike Polk
Sagebrush Consultants
Ogden, Utah