I've finally figured-out how to share files between my iPhone running Mixtikl, and other devices connected to the local network using Wi-Fi. Though it is a lot more work that it should be. :)
The way to do it was for Mixtikl to run as a HTTP server which broadcasts it's presence using Bonjour (see Apple's CocoaHTTPServer example to get you started!), and then you can browse for and grab files from it (e.g. saved .mixtikl or .partikl files) using Safari from any browser on your network! From Safari, select Bookmarks -> Show All Bookmarks, and click on the Bonjour tab. There is a Mixtikl entry from every Mixtikl iPhone on the local network; double-click on it to show the list of files on the iPhone, and select/save the files you want to your Mac!
The other way around, you're able to use Mixtikl on the iPhone to see files advertised by Mixtikl on the Mac (which also runs a HTTP server advertised using Bonjour); Mixtikl has a special view allowing you to select the server to use, look at the file list, and select the file(s) you want to copy-across to your iPhone.
Cool stuff; welcome to the Zeroconf revolution! :)