The only images I ever delete are the totally OOF and severely over- and under-exposed.
Anything I edit, I rate with one start.
The best of the day's shoot gets two stars.
At the end of the year, I take all my two-star images and upgrade 10-15% of 'em to three stars.
If I'm particularly proud of a given image, I might rate it 4 stars.... but this is extremely rare.
I can rate images up to 5 stars, but have yet to use that yet.
Sort? I create a file sub-directory and rename all the images with the same name. So if I were to shoot a rose, I would create a sub-directory called "Rose 2012_6_16". All the images would be transferred to there, and renamed (Rose 2012_6_16 ffff nnn", ffff being the original DSC filenumber and nnn starting at 001 and continuing sequentially.
I use ViewNX2 to quickly view and rate my images, and transfer them to Capture for initial editing.