As fluid as "guys" is, I try not to use it (often in vain, it is deeply ingrained in my vocabulary) because its counterpart, "gals" is not as fluid. This may seem kind of arbitrary, but thinking about this particular language foible, I wondered how most men would react to being called "gals" when in a multi-gendered group. I envisioned at least some recalcitrance, and so I decided using "guys" probably isn't the best thing to do, although like I said I'm not as strict with it as I could be. I also virtually never get offended when someone refers to a group I am included in as "guys" because really, I just have so many other things I'd rather rail against.
I think my example about "gals" is a vital one, though, and I'm interested to see if it would be proven out. Is there a double standard involved in this little word pairing? Is it troublesome that we default to the male of that pairing when talking about a mixed group? Sure it probably doesn't cause any immediate harm to, well, anyone, but it is something to consider.
I don't mind people who deconstruct and criticize our use of language. I enjoy it. I just don't really practice it myself all that often. And if pressed, will usually give way to a view I think is perfectly valid, because it is just not that hard to think about changing my language, and even sometimes a welcome challenge.