It is not automatic, but it is very simple. You load the Sonos Desktop Controller program onto you computer -- it mimics the hand-held controller. Once Sonos knows where to look for your music, you can download music into iTunes and then make Sonos aware you have done so by using the hand-held controller or desktop program. The only caution I have (and I don't think this is particular to Sonos, but more to iTunes) is if you plan to run different music libraries (as I do -- one compressed and one lossless) you need to make sure you have the correct library loaded into iTunes before synching with Sonos, so that you don't wipe out one music list and replace with another. Even if you do, thought, the solution is fairly easy -- get the iTunes library to the one you want, the resynch with Sonos. BTW, Logitech has just announced a new (or updated) distributed music system for the house at the CES. Don't have much info on it, but it might be worth a look.
http://www.logitech.com/index.cfm/172/4180&&cl=us,en