I have cleaned my condenser (do about 2-3 times a year) and I clean my filter once a month (I have dogs). Maybe I described my temp differential incorrectly, the air coming out of the ducts is usually in the upper 50's. So I assume this is a good temperature differential. It does use a lot of electricity to cool the house from 85-78, but it uses less than if I left the house at 78 all day. For instance, my thermostat tells me how many hours my systems runs in a day. It usually runs about 3-4 hours on a weekday and about 8-9 hours on a weekend. So I am using about half the electricity when I let the house warm up when we are not home.

I also have a big TV (65in 10 year old TV...so it uses more electricity than newer big screens) and multiple fish tanks (that run 24/7). So I know it is not just the A/C using electricity, but I think the bill is a bit larger than normal. The temperature is actually lower than it was two summers ago (average high was 99.2 for the month of July 06 and 95.3 for the month of July 08), so, I should in theory be using less electricity.