I have, for years and years, never found the need to use an usb device on my computer. This may be in part because the usb slots are all on the back of it, and I'm not that fond of crawling on the floor when it isn't necessary. I have configured the kernels for it, but never tried it out.
However, some time ago my old server decided it didn't want to do its job any more (not even occasionally). And suddenly, in the middle of the current renovating/moving thing, I decided that I needed my cv file. M offered me the help of his usb disk driver. Comedy ensued from this.
In the end I had managed to replace the disk in the driver with mine, and connected it. Next step was to look for it. M said: well, in Ubuntu it just mounts and you can use it. I said: that's usually not the case in Gentoo. Instead I checked the syslog, which showed no sign of having noticed a new usb device recently. Damn, I don't want to reconfigure the kernel just now. I read Gentoo's usb howto, checked my configuration, which seemed to have all bits checked that should be checked, checked lsusb, dmesg, and everything else I could think of. They told there were plenty of connectors, but no devices attached. I gave up and decided to use M's computer instead, the one with Ubuntu, which auto-mounts everything. How annoying. Surely I didn't break anything during the screw-loosening?
I was at this point that I started to think: did I press some kind of button or switch on the driver while I was working? I did, didn't I? The kind that has a '1' and a '0' on it. Check: sure enough, there is a switch, it is set to '0'. I switch it. Now the syslog tells me about this new, shiny usb mass storage device that has just announced itself. What a relief.
So the problem wasn't with Gentoo after all, but a perfectly normal user error, one not even Ubuntu would have been able to compensate for (I think).
 I need to unscrew this, where's the screwdriver? In The House! This screw is stuck, I need a pair of pliers, where are the pliers? In The House! You get the idea.