Heh, one of the most common things I see when reviewing code is PDO users realizing they can't "bindValue" or "bindParam" an array of values coming into an IN() clause.

Here's a decent example of doing it right:

https://stackoverflow.com/questions/14767530/php-using-pdo-w...

Here's one showing noobs how to do it wrong:

http://pdo.w3clan.com/tutorial/176/like-clause-in-clause-and...

Look at that blind implode function. Argh. It's the danger of copy/paste echo-chambers.