Booted off the 2009-08-13 test day live CD, there obviously was no ifcfg-eth0. There was no system-config-network that could be used to configure eth0 either (just the console mode app and I couldn't figure out how to do this with it), installed system-config-network (the GUI one) and managed to create the connection.
No matter what I tried (plain NM restart, NM stop - /etc/init.d/network start - NM start - NM stop), stopping NM brought down my eth0.
Thanks for filling this bug report.
This particular bug has already been reported into our bug tracking system, but
please feel free to report any further bugs you find.
Fedora Bugzappers volunteer triage team
*** This bug has been marked as a duplicate of bug 517229 ***
Niels, yes I noticed bug 517229 before submitting this one. Why I reported another one is that 517229 contains so little information (whether /etc/init.d/network was run for instance, and whether the connection was configured via system-config-network and had a ifcfg-eth0 file) that it's not possible to say whether it's the same issue. I *guess* the NM developers need that info.