@bjornhallberg
I'm currently using OpenHAB with a couple Arduino sensor nodes. It works great. It does everything you've put in your required list and then some: rules engine, slick android app and browser interface, email / push notifications, data collection and charts. The only missing piece is the GUI for scene creation, but it's in the works. Also, great active community.

Here's some videos and tutorial of what I've got working:

http://goo.gl/je6LzU

I was in the same boat as you. All these "Home Automation" platforms take a lot of digging into to find out where their shortcomings are, what they're capable of. Although I did not do an exhaustive survey of everything out there, I did look at a few on your list, and ended up with OpenHAB.

I'm a Linux newbie, so I won't be able to help out much with the Raspberry Pi gateway development. But I wanted to send some good karma this way because I'm really excited about it, and appreciate all the work you guys are doing.

I'd like to better understand how the Raspberry Pi gateway would work though. These are some of my assumptions.

1. The RPi runs a webserver, and presents all current sensor data as a webpage?

2. RPi also acts as the interactive button provider, so you can actuate Arduino outputs from buttons in the webpage?

3. Will there be data collection and trending? Is that what the cloud based service is? Can I use the RPi to send data to xively or similar services?

4. Is the RPi doing to act as a scene agent? So you can make conditions (if Node 5 PIR sensor senses motion) and take action (activate LED on Node 6 Arduino)?

I'm one of those waiting for the Raspberry Pi gateway. Very excited and grateful for the work going into this.

In the mean time, I got this idea from the smartthings site. Am I right that sensor types have to be pre-defined so that the gateway knows that to expect from the sensor node? If so , I would like to have a sensor type call "presence sensor". It'll be an Arduino running on batteries that sends a periodic signal to the gateway via nRF24L01. If the ping stops comming, it means Arduino is too far away from the gateway. Could be used to alert you when the dog has run out of the yard, for example.