Quite amazingly I had two e-mails arrive today pointing me to the same site, one via the Scott Hanselman blog I mentioned earlier and another from somebody commenting on an article called "It's a good time to be an embedded systems programmer." which I posted a few weeks ago.
In that I suggested that t might be a year before the PI caught up with the Arduino in terms of hardware support, but I was wrong. You can buy a PCB that allows you to use Arduino shields with your PI so effectively it has already caught up!
There seems to be a library of support routines available so it shouldn't be too hard to put together a fully working system quite quickly, certainly faster than making designing your own PCB or laying it out on Veroboard and hand crafting your on software.
Its 40 Euros, which is more than some of the shields, but it is reusable so can be used again and again, so I can see it being a useful thing to have around. Even when hardware support for the PI builds up the Arduino has a heck of a lead and I doubt it will be overtaken for years, so I don't think it will end up in the bin any time soon.
One word of warning, I am sure I read that the first batch of Chinese Raspberry PIs had a different pin out to the current ones which are made in Wales. This has to make a difference, but I am not sure if this is a showstopper or just something to bear in mind.
Either way take a look for yourself at http://www.cooking-hacks.com/index.php/documentation/tutorials/raspberry-pi-to-arduino-shields-connection-bridge