I find if you're going to write even remotely canonically, they can't not be mentioned. I prefer to keep them out of the story, but there's also a difference between featuring them a wee bit and them taking over completely. ;)

You will never find Castiel setting up house with Dean in my stories. Hehe.

And, yeah, part of what makes me puzzle the most is the fact that the same people who grumbled about the previous female insert characters are loving the shit out of Castiel. It's like they don't even realize they're pulling a double standard. But he's a great actor! He's compelling! Er.