I think the enthusiast will probably have to wait for the other shoe to drop. The EOS-M seems to be aimed at the consumer moving from a P&S. It has an iPhone type touch screen interface and simple controls. It can't be the only MILC that Canon are planning. I'd assume they'll have another model for photographers moving the other way, i.e. adding a MILC to their DSLR system. Sony, for example, have the NEX-3, NEX-5 and NEX-7.
The problem with the EOS-M (besides the fact that it won't be available until October) is that it's not particularly cheap, especially when you add in the EF lens adapter. You're looking at $800 for the EOS-M with the 22/2 kit, another $200 if you want the adapter and another $300 for a basic 18-55 zoom.
You can get an Olympus E-PL1 with a collapsible 14-42 lens for $295 (see
http://www.amazon.com/exec/obidos/ASIN/B0035LBRKS/bobatkinsphotogr ) and you can get an EOS adapter for about $25. You can't change the lens aperture and it's manual focus, but you've only spent $320.
I actually have the E-PL1. I'm sure the qulity doesn't match the EOS-M, but for me it's good enough for now. If Canon bring out a more advanced EOS-M with and EVF and a control layout more like a T4i, I might be tempted. I can wait.
Actually I'm more tempted by the G1X right now. Small, 28-112/2.8-5.8 lens, optical viewfinder, built in flash, digic 5 processor, iso 12800 and selling for around $700
for G1x see
http://www.amazon.com/exec/obidos/ASIN/B006UMM2BW/bobatkinsphotogr