Canon has delayed availability of the Canon EOS-M system until at least October 31, 2012 in North America.
Keep an eye
Both B&H and Adorama have October 15, 2012 as the day the Canon EOS-M begins shipping in North America. The first kits to hit the market should be the EOS-M body and 22mm f/2.8 STM lens as well as the Speedlite 90EX.
Early reviews for the first Canon mirrorless camera have been relatively positive. It's not an earth shattering advancement for the segment, but it does what it does quite well. The biggest issue people have had with the camera is an autofocus that isn't lightning fast. This seems to be a relatively common theme among mirrorless cameras. For people going from a PowerShot to the EOS-M, they're not going to notice. However, if you go from your 5D Mark III to the EOS-M, you're going to notice the slowdown.
I am looking forward to trying it out.