Donald Knuth was saying this how many years ago? It's got to be something like 10 years now. This is why he stopped sending out checks for people finding bugs in his books.
Most of Retail stopped accepting checks about 15-20 years ago, iirc. It was about the time laser printers and copiers came about that everyone realized how insecure they were. Now, banks are one of the few places that accept that form of currency.
Edit: Judging from the replies, my personal memories are incorrect.
Not in the US they haven't. I've certainly watched it enough to know the hoops they can jump through, the long method: Check is scanned by a machine at the register and a modem or network check happens to make sure the account is in good standing, they get the person's id and write things down on the check from it and then ask for a phone number. Makes me appreciate self checkout a lot. Some times they just scan the check and give it back which typically confused the heck out of the person who just wasted 2 minutes filling it out.
The security of checks have never depended on difficulty of duplication. Most places checks at least used to be valid if you simply wrote the right information down on an arbitrary piece of paper.