Eileen has posted about a fairly long life span for one of the certificates on her machine - http://blogs.technet.com/eileen_brown/archive/2009/01/29/a-very-trusted-certificate.aspx
If you want to find the certificate that will last the longest on your machine – PowerShell is there for you
Get-ChildItem -Path Cert: -Recurse | Sort Notafter -Descending | Select -First 1 | Format-List
use –recurse to dir through all of the certificates – the certificate store is exposed as a drive by PowerShell. Sort on the Notafter date & select the first. Format as a list to see all the properties.
Quicker than opening a GUI.
Read the complete post at http://richardsiddaway.spaces.live.com/Blog/cns!43CFA46A74CF3E96!2017.entry