I guess it's all about being seen by Windows as a storage drive that's the key...
My S65 & SX1 phones both have MMC/RS-MMC therefore a card reader is perfect for MP3s ebooks & the like.
(I have a USB 'stick' that your SD/MMC/RS-MMC plugs into, is the size of & works like a regular USB memory stick/card reader. I'd strongly recommend one if you can find them, saves a bunch of cables for t'camera etc when travelling).
However my RazrV3(internal mem) & Zodiac 2 Palm based PDA(SD/MMC) does not appear in Windows without installing their software (thus negating the use of MC) & therefore mp3s etc have to be sync'ed via their own software.
Even better they ALL use different proprietary software to SYNC with my PC, even my 2 Siemens phones. Best of all the only common interface appears to be Outlook & that just loves multiple phone sync'ing [/sarcasm]
So for MC to work with everything, it would need to be compatible with:
(by compatible I mean not only moving files but sync'ing)
Palm
PocketPC
Symbian
Linux Handheld (A few handset/PDAs are due out soon)
mRouter
Popular mobile manufacturers
(EG Nokia, Sony Ericsson, Siemens & Motorola at the very least)
etc etc
THEN how exactly will you sync it, via Bluetooth, Datacable (USB or Serial), irda or some other method.
If you want 'mobile MC' then it has to work with all of the above also...
If it has memory only onboard then chances are it'll want it's own sync'ing software.
BUT, looking out for an SD/MMC/Other Memory Card solution in most gadgets I buy seems to guarantee general inter-operability & MC compatibility.
Which is fair enough, I doubt even Steve could keep up with all the gadgets as they are released.
And me, I find it much less hassle taking the card out & transferring it to my PC. Besides with a 1-2Gb SD it's much faster outwith the native device.
The problem in the future are things like the Palm LifeDrive, as it's got it's own teeny tiny hd, just like the mini iPod, try hotswapping that & seeing how far you get...
It's a helluva task!
Mind you, if MC could do all this & become the Swiss Army Knife (yes I do know there's a 1Gb USB swiss army knife out now lol) of all things music, video, image, handheld, phone etc then it's got a much better chance than Brain of taking over the world!