Well I finally couldn't wait any longer for an ARM Linux board (my Pi isn't due until the end of June), so I bought a BeagleBone. 
(This post is about technology. I am not interested in "A is better than B" arguments. Horses for courses.)
It's a very nice board, much more like an Arduino in concept than a Pi -- the two rows of female headers give it that feel. Farnell provided their usual (in my experience so far) perfect quality of service and delivered it the very next day --- http://uk.farnell.com/circuitco/bb-bone-000/kit-dev-beaglebone-cortex-a8/dp/2063627
The power design is particularly noteworthy, given our recent discussions about polyfuses. The BeagleBone uses a TPS65217B power management IC (PMIC) to generate stable supply voltages regardless of input power, which can come from a barrel connector or from the mini-USB.
The mini-USB itself deserves a mention, as it's impressively multi-functional. In addition to being an alternative source of power, it provides a front-end two-port USB client-side hub --- this is entirely unrelated to the separate host-mode USB type A socket which is also available. One port of this hub goes directly to the TI AM3359 SoC, while the other port connects to a dual-port FT2232H USB-to-serial converter to provide user-host communications (Linux console by default) and JTAG debugging simultaneously.
The SoC USB connection to the front-end hub works in one of two modes which can be toggled at will at any time: it either presents the SD card as a mountable USB storage device to the host, or it provides an Ethernet-over-USB networking interface which yields an extremely simple quick-start. (This is additional to the BeagleBone's normal 10/100 Ethernet interface, which is directly implemented in the SoC rather than hanging off USB.) It all worked immediately using my Gentoo machine as host, providing full IPv4 and IPv6 connectivity out of the box.
Which brings me to BeagleBone and Raspberry Pi. These two devices are very different, enjoying different strengths and suffering different weaknesses, and their most appropriate applications would naturally fall in different areas because of these differences. I'm interested in how the best features of each could be combined to provide better functionality than either does alone.
I already have one idea in this area.
The BeagleBone doesn't provide an on-board graphics interface (despite its SoC containing a PowerVR GPU), and as a result, if you want direct graphics you have to buy a "DVI-D cape" containing the interface circuitry ("cape" == BeagleBone daughterboard). The trouble is, that cape costs more than a Pi Model B!!!! 
Which of course provides an ideal opportunity to combine BeagleBone and Pi, since the Pi could handle the graphics side while the BeagleBone does most of the computing which suits its Cortex-A8 nicely. I'm currently thinking what the best way to achieve this might be, but one simple way is available out of the box since X11 is inherently a networked protocol.
This is obviously just the beginning, and I'm quite excited to see where this combination might lead. 
Morgaine.
