If you're still wondering exactly what OpenID is or how it works with apps like Basecamp and Highrise, check out ScreenCastsOnline's free, 15 minute screencast about OpenID.
The video includes a section that demonstrates how to obtain an OpenID (using MyOpenID as a provider) and then shows how to use it to access both Basecamp and Highrise.
It also shows the new Open Bar in action. If you've got both a Basecamp and Highrise account (or multiple accounts in either), you really oughta get onboard the OpenID train. It makes navigating between your accounts way smooth.
Related: About OpenID section at 37signals.com.
