I've used costco's a few times now. Only the new(er) locations have the processing, and the closest one to me is 20min drive (Each way). Then they do NOT do the 1hr processing for digital, even though it says they do. But, at that price it is hard to beat, so, I save up and do a bunch at a time.
As mentioned above, their 4:3 -> 4:6 cropping is not the best. I've even cropped some myself using paintshop pro and the cropping tool, yet they still get them a bit off. So, best to have about a 5% margin of error (leave a bit extra around the borders) or you'll have to deal with getting them reprinted. I'd be happier if they'd just leave a blank border and get the whole picture in--uncropped. But, then you'd get a bunch of amateurs complaining about that. Should be an option you can check off on the kiosk!
That, or, I wish my camera had a 4x6 or 5x7 compatible ratio now. It's a P.I.T.A. to resize them each time.
One cool thing I did (I think) was using paintshop to crop a photo and then on the blank border I added a 'Happy Holidays' comment. Then saved the pic and got them printed at costcos. Looks very professional (the printing at least, not the photo!).
I'm pretty sure @ .19/4x6 pic it's very competitive to printing them on inkjet (maybe even cheaper?) and the quality is definitely better than my current printer. Not sure about the 4800x1200 models.