I had a top overhaul  done a few years
  ago and, afterwards, oil consumption was so bad, the mechanic agreed to redo
  it at no charge.  That helped, but did not cure the problem.  I still burn
  about one quart every two hours more or less.  The oil is always black -
  indicating blow by (I'm told),  I complained on and off for months to the
  mechanic who did the work, but I finally gave up and am just living with the
  problem - and using a different mechanic.

Matt, John, et al,

 

High oil consumption is not a good thing.  If I remember correctly, my Lyc 320 engine manual indicates that operations should not be conducted when oil consumption is in excess of 2 quarts per hour.

 

Here is the text from:  http://www.lycoming.textron.com/main.jsp?bodyPage=/body.jsp

 

"Tips from the Hangar"

QUESTION — What are the dangers of operating an engine with high oil consumption?

ANSWER — When excessive amounts of oil get past the rings, there is danger of the ring sticking or breaking with a dramatic rise in oil consumption. Then oil soaked carbon forms at a fast rate. At the same time, the presence of oil in the combustion chamber has the effect of lowering the octane rating of the fuel. Operating temperatures go up. We have now set up conditions inviting detonation and/or preignition.

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I am peeved with my stabilized rate of consumption of 1 quart every 5.5 hours or about .2 quart per hour.  Such usage is not maximizing best power.  I have tested for high crankcase pressure and found none.  I am intrigued by Chuck Moon's sump leak and I will check the induction system for the presence of oil.  Another possibility is leakage thru loose valve guides.

I was further depressed by Bill Harrelson's Latin American trip report of virtually no oil usage.  Perhaps he just didn't remember adding oil because of excessive Margarita consumption?