How should I cull photos and decide which images to keep?

I don't know if this is a great system, but here's what I do:

1. After the shoot/session is done I immediately sort through every frame I took looking for the 'keepers.' I do it this way because for me it is easier to choose to keep the great shots than it is to delete the borderline shots... That may just be me. :-)
2. Next I sort through every frame I didn't put in the 'keepers' pile and look for anything that is bad enough to just trash immediately- usually there are a few out-of-focus or technically flawed photos that I didn't delete 'on-the-fly' which get taken out back behind the barn and put out of my misery.
3. I then look through the 'Keepers' and see if there are any 'holes' in the shoot that I will need to fill with the shots that weren't good enough to make my 'keepers' pile, but weren't bad enough to trash... Call it my 'marginal' pile if you will. If there are holes to be filled I then pick the 'best of the worst' to fill in those holes.
4. I post-process all the 'Keepers.' If it's a personal session I post 'em, if it's a professional session I work with the client further from there to close the contract. For client contracts this is it. I keep both the 'keepers' and the 'marginal' shots forever and get ingested into my backup solution (which is an entirely different process).
5. After some time has passed (I usually do this every month for any personal work that happened 3 months prior in order to allow myself a bit of perspective) I re-examine the 'marginal' pile to see if time has changed my initial impressions of those photographs... Usually there are a few in the 'marginal' pile that I like enough to keep. The rest are shown no mercy and get to go to the round file from there.