OpenelecI bought a fresh memory card, supposedly a class 10 capable of 20mb/s.
I then downloaded and installed a tool capable of writing linux disk images, Image Writer for Windows. After that I grabbed the latest image version of openelec.Go to http://openelec.thestateofme.com/ and scroll all the way down and download the most recent zipfile. Extract it and use imagewriter to put it on the SD card. Pop in the card and power up your raspberry.
Now I can't tell you how quickly this boots because by the time I'd found the TV remote and switched to the right channel it was already running. XBMC looks just like it does with raspbmc. Playing content is a matter of checking the sound output is correct in the settings screen and adding a source. I used PnP which my synology supports.
Playback was smoother than raspbmc. Raspbmc has the occasional stutter on higher bitrate mp4 files, Openelec is as smooth as 18 year old scotch.
If you run into problems, just go here.