So, just hearing about this. Seems like I have to replace all integrations?

This only impacts those Integrations that use SuiteSignOn. For us this would be integration with OpenAir and Avid. Other integrations that don't have a SuiteSignOn record should be fine as is.

Not sure I know or see how to determine which integrations are SuiteSignOn...

Under Setup > Integration > Manage Authentication is where I can see and manage all of our SuiteSignOn records.

I mean, I see the integrations there, but I see nothing that tells me whether or not the integration is one that uses SuiteSignOn.

If there's a SuiteSignOn record then you are using SuiteSignOn, assuming that it relates to an active Integration point. We have one for example for Adaptive Planning but we no longer use Adaptive so I don't have to worry about updating that. If you're integrations are all setup under Manage Integrations these are not SuiteSignon

Ugh - finally clicked. Thank you!