This is broken for me too, and only broke after the May 26 update to NetworkManager (0.8.999-3.git20110526.fc15).  See bug here too:
https://bugzilla.redhat.com/show_bug.cgi?id=708626

It "works" for wifi only if you delete all the things as said below, but if you try adding a VPN connection it breaks again.  It is very fragile :-/  I wasted many hours on Sunday trying to resurrect my laptop.

On Tue, May 31, 2011 at 2:53 PM, Tim Evans <tkevans@tkevans.com> wrote:
On 05/31/2011 06:17 AM, Michael Schwendt wrote:
> On Sat, 28 May 2011 14:31:44 +0200, AM wrote:
>
>> This morning updates of Network-Manager1.0899.3.git20110526 killed all
>> networks, no way to connect any more, I had to downgrade to previous
>> versions
>
> Apparently, there are major issues for users. Just look up the update
> ticket in bodhi and the bugzilla ticket(s).

I had to remove /etc/sysconfig/network-scripts/ifcfg-Auto* then re-start
NetWorkManager. This solved the problem I saw after pre-upgrade F14->F15.

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