As for the pros, if done right (a big if), you can make a very "stealth" install with great performance, even rivaling the best freestanding speakers.

I think that the biggest con is that the average stud cavity doesn't make a very good speaker box and so, for high performance, wall preparation/construction is definitely a factor.

There is also the issue of finding good, shallow-mount driver units (especially woofers) but there are some interesting approaches out there.

Feel free to bump me an email if you want to speak in more detail.

-Chris