Efficiencies for them is typically 90% and up,  unless you _need_ a 
sinewave
for some reason,  so it doesn't amount to all that much.
 RS> I believe that the larger ones waste more than the smaller ones 
 RS> do.
What are you basing this on?  I don't recall having heard anything to this
effect before.
Hope you don't mind my butting in here. I am an electrical contractor 
dealing largely with RE systems. My personal experience is mostly with 
Trace inverters, as they appear to be the most popular, and by my 
experience, the most reliable. (I didn't mean that to sound like a 
commercial, it just happened). They claim 90 percent efficiency in the 
"modified sine" (actually modified square) inverters. I have worked with 
inverters that were less effiecient. Also, the "true sine" inverters are 
less efficient, though the numbers climb a bit each year. A modified sine 
will do for most things, including computers (but not laser printers).
Lately many RE homes are wired only for AC, through an inverter. The 
advantages include use of standard connectors and circuit protection 
equipment (except for the batteries), as well as smaller wire (much less 
$$). My personal preference is to include at least two DC circuits for 
lighting in any case. Just because it is still possible that your inverter 
may break down at some point (Never trust a machine 100 percent).
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