I've seen them before, and did seriously consider using one (can't remember which one in particular) when I was looking for a particular Tokai or something.
But ultimately it did seem very complicated and the language barrier threatened to be..... well, a barrier. :?
You do see some amazing stuff on Japanese sites, but there's so much background information (such as terms and conditions...) which is really difficult to decipher. It just makes me wary. Maybe I worry too much - but I have bought lots of things from Japan, I'm just more comfortable in the familiar surroundings of eBay.