Yes there is a big waiting list, I got myself on the list within the first day or two of the announced availability and just received mine.

The APC computer is indeed interesting, but since they are not yet available it's hard to say if a Debian install will be easy.  I'll leave that to others.

There are a few other options like the Sheeva Plug, Beagleboard, etc.  The gateway code is pretty distribution agnostic, but most folks run it on Debian or Red Hat derivitives.   So if you have a "beefy" enough ARM processor and a Linux OS, it can probably be made to work.

Since the UDR56K already has the processor board, no external board will be required.  It will not only be able to run the gateway and half-duplex access (hotspot) through it's own radio, but I'm fairly confident that you could run a couple of USB connected node adapters and build a mini-stack.  Since ircDDBGateway also talks to Icom's RP2C, you might be able to integrate the UDR56K to add say 56K DD and let it also run the RP2C, eliminating the need for a separate computer.

One repeater configuration may be to use an external receiver with a node adapter and dvrptr board (I would probably not use the soundcard solution) combined with splitrepeater to build a full repeater with the UDR56K.

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