This is why I love the Internet: because I can get lots of perspectives on an issue without even having to get up off the couch!
I should have clarified that I don't think signing with your baby is a bad idea. The conversation we had with Bryan's aunt was interesting, but hers is just one perspective among many, and based strictly on her own experience rather than on data (as far as I know). She works with preschool- and kindergarten-aged hearing-impaired children, so what she's observed in her field doesn't necessarily have any bearing on our situation as parents of an infant with normal hearing. Even though she feels strongly that using signs with your baby isn't wise, the large majority of the data I've seen suggests otherwise, and so it seems to me that signing with Camilla would have, at worst, a neutral effect on her verbal development.
However, and with the caveat that I'm not educated enough to analyze the data any more than cursorily, I'm not convinced that using signs (by which I mean ASL signs or the like, not gestures that normally accompany verbal communication) to communicate with our developmentally-normal child would have any positive long-term effect on her verbal development or IQ. (I'm especially skeptical about the IQ.) And in the absence of evidence of a strong positive effect, I don't feel it's imperative to teach her signs in order to do the best for her.
Which means that the important question when considering whether to use sign language is: will it make life better or easier for our family? The answer to that is a complex equation involving many variables, including: (1) the amount of time and effort needed to teach signs and use them consistently, (2) the amount of time between now and when the Billa becomes verbal enough to communicate most of her needs and wants, i.e. the amount of time during which signs would be very useful, (3) the amount of frustration she and we would experience if we didn't use them, and (4) the amount of enjoyment we would get out of using them and seeing her use them.
Considering the relative largeness of (1), the expected smallness of (2) and (3) (based on her personality and her ability to communicate non-verbally without specific signs), and the "ehhhh" feeling I get about (4), I'm thinking we're not going to do it. If the circumstances change and we think she is getting frustrated with being unable to communicate, we might reconsider. Meanwhile, I'll lend the sign language book and DVD to anyone who thinks she might want to do it with her baby. Hey! Anyone want to borrow it?
On a complete non sequitur, a public service announcement for all co-sleeping parents: Before appearing in public in the morning, be sure to check the mirror. It is possible for items to exit your baby's nasal passages and bond themselves to your face in the night. No one looks good with a huge dried green, uh, booger decorating her face.
(This very useful piece of advice may or may not be based on my own (totally gross) experience.)