I've put together a short review of the Yongnuo ST-E2 in comparison to the Canon unit on my blog. I found the recycling time on the Yongnuo to be slower than the Canon unit, which is a problem. Otherwise, it's a nice piece of kit however:
http://sarahmcdonnell.co.uk/photo-gear/yongnuo-st-e2-speedlite-transmitter-review/
http://sarahmcdonnell.co.uk/photo-gear/yongnuo-st-e2-speedlite-transmitter-review/