Ok guys, first off, the US Postal service can't NOT deliver. UPS and all the freight companies can refuse to deliver to any address. The postal service HAS to service if there is an address, they got no choice.
That's not true. I've personally been in a situation where the post office decided not to deliver to my house. They also didn't tell me that they weren't delivering, even after I went to the post office and asked what the deal was. It took months to get it straightened out. Eventually, there was a story about a "bad dog" and such, but it took a long time and some extra effort on my part to figure that out since when I would go ask they would tell me "There isn't a problem".
Now, that said, they may not be able to choose areas and say "That's not in our delivery area, nobody out there is going to get mail". Maybe. I'm not even convinced about that, because I think I've read about little stores that are the closest thing to a town for miles that act as the local post office, and anyone in that area has to come to the store to get their mail.
I think the USPS does a good job overall. With the exception mentioned above where they stopped delivering to me and wouldn't explain it, I've had very good experiences with them.
I don't really care if they deliver on Saturday though. Personally, if they want to drop one day a week, I'd just as soon them do it on Wednesday or Thursday. If you drop Saturday delivery, since they already don't deliver on Sunday, it means a 2 day period with no delivery. By dropping a day mid-week, there are still 2 days where they don't deliver, but they aren't back to back.