Re:Interesting (Score 2, Informative)

For XML (users list and playlists responses), Whamb uses CoreFoundation's API, which has an option for binary property lists. It's about 2-4 times smaller than plain XML. WSD uses plain XML tho, but it's not really a problem on a local network anyway. Mac OS X has a great support for plist/XML (all apps use it), it's so useful and efficient for trees and complex data... maybe you need to review your opinion about it :-)

For the scalling problem, I just discovered it's a limitation to CFStream's API (can't send more than about 256K of binary XML). It's gonna be modified in 1.1.1 to use a less specialized way but without any limitation, until this is fixed in CoreFoundation...