I think it's about time I phoned support again.

Wow. I think you are going to get elected poster child for Zaurus Evil Badness. It sounds like Sharp has been somewhat responsive, but that's little joy if the thing has never been usable. Yes, I see a fair number of threads on the sourceforge lists about problems with various SD/CF cards/brands sizes and with removable media filesystem/removal issues; methinks I got very lucky with the Memorex 128 CF card I got for the 5000d originally.

It's a hard row to hoe given that the 5000d was a developer/prerelease product, but given the complete lack of usability you've experienced (while essentially playing by the rules), I would keep hammering support in the hopes that some brilliant individual decides it would be less resource-intensive to exchange you a 5500. Chances of that? I'd say very low, but you are in a crummy spot, otherwise. Wish I had more to offer!