Yeah, I know all about the Squeezebox devices and the SlimServer. Exactly what you have described has crossed my mind as a solution too, before, and for other applications too (email etc). My concerns from a media standpoint have always been:

*Guaranteed upstream bandwidth from my home... here in the UK SDSL is not widespread. I've not actually tried this though...
*Guaranteed availability of my home network connection

I'm still considering the squeezebox as a home solution but can't see it working when I roam, for the above reasons...