I think it doesn't make sense to compare the Yun to a rPi. They are different tools for different jobs. One is a microcontroller with some nice microcomputer functionality, the other is only a nice microcomputer.
I have three Yuns, two of them serving as webservers of a multi-threaded database application that serves different websites for all the appliances I want to control, including logging of the status of the appliances, user actions, and a few environmental parameters where the controlled appliance is a heating or cooling device. This includes background jobs, that make sure that the user input is properly communicated to and acknowledged by the appliances.
All this on the Atheros side, functioning under real world conditions for half a year now (one of the two webservers has currently connectivity issues though, see the thread for details). The Yun without the connectivity issues is up for several weeks now, without reset.
Some appliances are controlled via http directly on the Atheros side.
Some other appliances are controlled by a half a dozen remote Arduinos that communicate with the MCU on the Yun via a nRF24 network. I use the bridge, but not the client/server model, rather .get() and .put(). I found that more transparent and practical.
And yes, I also develop in parallel on a rPi, as "Plan B", and just for the fun of it, just in case the whole database application / webserver architecture on the Yun's Atheros hits it's limits. I would then use the rPi as the webserver and control an Arduino UNO with the rPi to access my nRF24 network. But, knock on wood, the Yuns do it all so far.
I'm sure what I have is not the most complex and sophisticated application for Yuns, but I think I came quite far - 9 months ago I didn't even know what a microcontroller is and I had absolutely no contact with a unix system before (I work in IT though for almost 30 years).
So yes, the Yun is very suitable for beginners. Even if one has absolutely no clue about microcontroller and microcomputer, unix in general, openWRT in particular, forgot everything they learned in school about resistors, LEDs, etc., but is eager to learn, and determined to get things to work.
Bottom line: I would not agree that the Yun is beta. It's IT though. Software eventually works, hardware eventually fails. What keeps it interesting, and everyone of us learning, every day.
jafrei