Once you establish a pattern, stick to it. This one was pointed out by @deeann and @geekosaur, and I had forgotten how awful it really is, I’m so used to it now.
First, Apple decided that the “Save to PDF…” button needed more options, and instead of replacing the command button with a proper drop down menu, they added a glyph to a command button:
I really, really hate it when people break standard controls like this, especially OS vendors in global dialogs (and in this case Apple is as much to blame as the usual offender, Microsoft). Predictability is a key tenent of usability: once a user learns how a control behaves, they expect every similar-looking control they encounter to behave that way. This example is particularly bad, as there is a standard control that does exactly what they want.
Full disclosure: I’ve had occasion recently to re-design a drop-down, but it’s for an extraordinarily specific purpose, we’ve styled it very differently from the standard, and use them in enough places (a sort of global-to-System Center) as to establish a pattern. Still, we all agree it’s a gamble and will be tested before it’s released.
Of course, Apple just made a lazy, arbitrary decision and called it a day, something they do too often for my taste.
That’s not the only problem with this dialog. Look at the arrow to the right of the Printer: drop down:
What do you expect it to do? @geekosaur assumed it was a list of recently used printers. I think that’s an entirely fair assumption. It’s not correct though, as the arrow serves as an expander to reveal more printing options and show a mini-preview:
So why the hell is it next to the drop-down? The proximity creates an implicit tie between the two controls, even though they are not functionally related at all. Here Microsoft gets it right, using a pattern specifically for expanders (the chevron) and often giving it a label like “More options…” I like them a lot; here’s a particularly good example, from the Vista global Save dialog:
These are fairly minor, and fairly easy to figure out, but I really expect more from a global, OS dialog, so it graduates to an EPIC FAIL.