I use a program called airfoil to stream flac/shn from my mac to my airport express using play and cog. This has allowed me to stick with flac on the mac rather than going to alac. Really simple program that works well, although not free...
http://www.rogueamoeba.com/airfoil/mac/
Interesting. I like still playing everything in iTunes, one reason being the free Remote iPhone app that lets me control iTunes from anywhere in the house while Airtunes streams it to my system. I wonder if Airfoil, Fluke and Remote would all work nicely together.
One little catch is that I put shows on my iPod in the same ALAC format I use on the computer. So keeping and playing everything in FLAC on the computer would be only helpful if a) I could play FLAC files natively on the iPod or b) I could convert FLAC to an iPod-friendly format on the fly when synching the iPod.
I think the program Rockbox would accomplish option A; and I know iTunes will convert files when synching an iPod but I don't know if it would convert FLACs that you are playing right within iTunes with the help of Fluke.
This will only really be a big deal when I run out of HD space, which is not imminent.
I'm sure I've said it many times, but I convert everything to apple lossless. The only downside is re-tagging everything (and saving 2 separate copies in different formats, each in duplicate).
Yeah, that's what I'm doing currently. Except for, like you mention, the duplicate storage requirements, it's been fine for me. Even FLAC files that are tagged already when I download them (most aren't) keep their tags after I convert using XLD. And all the CDs I've been ripping have been going straight to ALAC, so no problem there.