I worked on a couple interesting stored procedures at a client this week that dealt with parsing & building XML data. Complex types turned out to be a little more challenging than I realized. Or, to put it another way, I realized my SQL skills when it comes to parsing XML were inadequate when dealing with a complex type.
I spent almost half of my Friday looking for an elusive error in one of my stored procedures that, of course, was working on our development environment. It led me to discovering something I was unaware of in regards to how SQL Server evaluates QUOTED_IDENTIFIER.