[fudster]

Hey thanks everyone - and sorry for disappearing for a few days. I was wrapped up doing a deployment last week.

I've checked the console for any sign of what might be causing this, but there's nothing to see.

I've been watching closely, and it seems pretty predictable - when I make a change in OmniFocus on the Mac (especially for the first time in a while), within about a minute the dialog comes up. I think OF is attempting to sync because of the recent change.

As far as interactions with other programs:
I had Lotus Notes 7.0.2 installed for over a year, and this exact same thing happened with Notes: "Lotus Notes wants to use the login keychain". It was a known problem with Notes - a real PITA. Since upgrading to Notes 8.5 (which is quite dandy, I actually don't mind it), the problem has gone away with Notes. I wonder if Notes 7.x toasted my login keychain or its settings.

I also have 1Pasword installed, and I'm long overdue to upgrade it to the current version. I've held off because there is some work to adopt their new "Agile keychain" mechanism, and I think it'll take a little time. So I've been saving that upgrade for a weekend when I have an hour to spare.

Andrew, I did indeed rule out the keychain-specific settings, and ruled them out. Just for grins, I also checked on my other keychains, there is one for 1Password and one for System, both had timeouts and I removed them. I don't know how this would make a difference, but I'm reaching here.

And there seem to be a couple more things I can try - I'll try creating a new login keychain as sfkeydel suggested, and I'll upgrade 1Password. I'll report my findings back to this thread.

Thanks again everyone!