Once a week if the weather is OK on the weekend. I do not wash it during the week because I get home too late, and I'm tired. If it's raining all weekend, it can wait 'til the following weekend.
I do check for bird droppings and tree sap or whatever very carefully. I don't let stuff sit that could harm the paint. If I find anything like that, I use a QD and MF towel to remove it before it sets in.
Personally, I'd love to have a freshly washed car all the time, but I'm not sure anyone other than Accumulator is careful enough to wash their car constantly without causing some swirling. I think for me once a week is plenty.