BeagleBone is nice and a good option for controlling an arduino. It is approximatly twice the price, but available.
But RPi has much more graphics processing power than the BeagleBone (or nearly any other embedded system) and a graphics output. That may not be improtant to some people, but even within the arduino community that maybe useful
One thing i have to agree with is- I rather pay more now, than few quid less and having to wait till Kingdom come !!
Plus there is this coming soon A13-OLinuXino - Open Source Hardware Board. Knowing Olimex previous products, this wont let us down... Only this is doesnt seem to have a dedicated graphic board( ?!?Am i corrrect there ?!? as they mention Mali400 MP as graphic acceleration) but has an A8 @ 1Ghz
Those Olimex guys do some nice boards.
Rob
The Arduino IDE seems to run really well. As far as Java apps go, the Arduino IDE is pretty light. The Pi would definitely make a good Arduino programming platform for students to learn on.
I am planning on using the RPi like the way couple others mentioned, off load the Ethernet and SD functionality from my Mega, Since the Ethernet shield can't do both server and client. I currently use 2 Ethernet Sheild, one on Mega to server web page and the other on Uno to send emails. If RPi can do both, that will be awesome !