Grumpy_Mike:
No I was saying that the so called low cost of the Pi was not so low when you have to buy a keyboard, mouse, HD TV, SD card and power supply.
That's a good point, and it would probably triple the cost at least if you had to go out and buy all the standard peripherals to get them to work.
But you don't always have to. I haven't bought anything for the one I'm using -- I had a spare 8GB SD card, and I'm running it as a network server, so it sits on my LAN and I use ssh or telnet from my laptop or desktop instead of a dedicated keyboard and/or monitor. I'm powering it from a USB hub, so I didn't even have to buy a power supply (although I've ordered one anyway... $5 from China on ebay. I'm such a cheap-ass.)
Other people may well have spare keyboards and mice laying about. I have whole closets downstairs with crap like that in them. I get nervous going down there though, I have dark suspicions about what may have been breeding down there.
The glass half-full view is looking at what you do get -- Ethernet port (on the "B" model), 2 x USB host ports, SD card slot, 2 x video, audio, some GPIO breakouts, an ARM 11 with 256MB of RAM -- and a couple of ports I haven't figured out what exactly they might be used for (cameras/video devices?)
How much are you going to have to spend on add-ons to get an Arduino with all of that (even the bits you can get)?
Grumpy_Mike:
In England it is a tale of how gullible people can be when offered what looks like a low cost bargain but then they have to buy all sorts of extras to make it any good.
OK, at least I understand the point you were making now.
Actually, I think embedded Linux devices complement the 8-bit Arduino class devices nicely. While there is some overlap at edges, they really have different strengths and weaknesses. Not every application needs hard real-time, not every application needs to do SSL. I've worked with embedded Linux devices in various situations for quite a few years now, so I have a fairly good idea of what they can do already. What knocks me out about the RPi is the breakthrough price point.
And of course, the thing about real-time (which seems to be your main criticism), is "how much" real-time do you need?
Garden variety Linux distros do what is sometimes called "soft" real time. It's got micro second timers, and if you program your app carefully, your delays will be no shorter than the timeouts you have requested.
If you need to improve on average time latencies (rather than worst-case), it's easy to bump the priority up.
If you really need "hard" real-time (i.e., genuine guarantees for worst case latencies), you recompile the Linux kernel with something like Xenomai, RTAI, or RT Linux (Xenomai - Wikipedia). Then you get a RTOS with guaranteed latencies in the order of 15 usecs or so.
I would be surprised if Xenomai has been ported to the RPi yet. But I wouldn't be surprised at all if it done in the reasonably near future -- it is running on fairly similar ARM boards already, and the Xenomai team is pretty active.
I personally think the RPi is going to attract masses of development interest because of the bang for buck. I'm already planning my next RPi project (which will have an AVR chip on a daughterboard, if that will soften your grumpy heart even a little :-).