Well 'round here all of my retailers still have plenty of manned aisles in addition to the self-check. Your points about product lookup and bad bar codes are valid, and why I'd be surprised to see any store do away with manned checkouts entirely. At least until we get to a more mature RFID technology.

Personally I like the option that many of the Giant Food stores have near me, which is a self-check scanner that you carry with you while you shop. If I pick something up with a bad bar code I know right away, and can just select another one. Label-printing scales in the produce aisles make it easy to price produce right away also, since the code is typically on the price posted in the product bin.

Also, everything is scanned and bagged before I go through checkout. All I have to do there is get help with a few random items (e.g. ID validation for booze), scan coupons if I've got them, and run my credit card.