I can recall one seasonal restaurant (Nantucket, MA) that "forgot" to bill until the following spring. I disputed the charge with the credit card company; they had put through the later date as "date of transaction", and, while I had consumed the meal, they screwed up, and commited fraud (IMHO) in an attempt to collect.
Another time I purchased a gift cert (loaded debit-card type), for which the restaurant never ever charged me. I got the iDine miles (bonus and all!) for it based upon the credit card slip I sent in, but the restaurant cancelled the balance on the card (I had used part of it) thereafter.
I had one restaurant double bill me about a year ago. The credit card company was very nice about it - rep told me that since it fit the profile of a duplicate billing, and was a small amount, she could credit me then and there without any followup at all. ^

When I lived in Queens there was an Irish pub which I used to frequent, mostly for Sunday brunch. Restaurant policy: tip line heavily X'd out and after tax amount written in by server before bringing tab to table.