As a long time Media Jukebox user and an iPhone owner, I keep looking at purchasing MC and then backing away since it doesn't offer enough more over what I already have in MJ. I hate itunes, but understand the issues of the closed versus open devices.
I'm sitting here staring at itunes "Determining Gapless Playback Information" as I have to periodically rebuild my itunes music library from MJ. It takes days.
If MC had just a little bit more iPhone support I would take the plunge and convert everything to MC.
1) Export playlists into itunes
2) Support from a library server
You may want to look at MCiS.
http://yabb.jriver.com/interact/index.php?topic=51734.0I use this to sync my MC library to iTunes and then use iTunes to sync to my iPods/iPhones/iPad.
In addition to keeping the iTunes library in sync with MC, you can also sync playlists, ratings, last played dates, etc.