I've transferred my iTunes library from my netbook to my laptop.
In doing so it occurred to me to try sync'ing some items to my iPhone from my laptop and some from another PC as I'd previously seen a hint this was possible.
Turns out it is.
So I now sync podcasts & apps from my laptop, and music, audiobooks, movies & photos from the family PC - which contains the masters anyway.
This has released GBs of space on my laptop as I only had copies of the music, audiobook, movie & photo files on the laptop so as to sync them to my iPhone.