You got it...at least the way most of here measure efficiency, i.e., how much sugar did we get out of the mash vs. how much was in the mash. Once you get the wort in the kettle you're done with that phase and everything following (boiling, siphoning, etc.) is unrelated. I'm guessing the average is ~70% for homebrewers. With tweaks you can get it higher, or just up your grain bill to compensate for efficiency.
However, there is also 'brewhouse efficiency' which commercial brewers use and I learned a little bit about last weekend while touring a brewery with some other hbt'ers. In that case, they look at the total amount of sugars in the grains (like we do) vs total amount of sugars that actually make it to the finished product (not like we do). This takes into account boiling/evaporative losses, line losses, deadspace losses, bottling losses, etc. So when a brewhouse says their efficiency is 70% (apparently an average #), it's would probably be more like 90-92% the way we measure it (sugars extracted from mash tun).
The Kaiser will correct me if erred in my explanation.
