Japanese for busy people. (Yes, I know you all hate it, but oh well.)
JFBP vol. 1 says that 'uchi' is used in regards to your own house, eg watashi no uchi, whilst 'ie' is used for anyone else's house, eg Tanakasan no ie.
(Sorry, still not got round to fixing my OS, so Japanese input doesn't work
I will fix it later or start using Japanese Word Processor.)
Anyways, that was what JFBP said, but may be wrong. I agree though, that they are interchangeable. You shouldn't be penilized for saying 'tomodachi no uchi'. Meh, whatever.
Later.