Perfect Forward Secrecy (PFS) has garnered widespread publicity in recent months thanks to Snowden and the NSA. As a result, an increasing number of websites and email service providers have been pushing for PFS to provide better security to their users.
PFS protects previous key exchanges even if the current one is compromised.
Unfortunately the same cannot be said about current popular IPSec VPN clients. Neither of the ones I tested – all of them from recent distributions including Windows and OS X – offered PFS out of the box, meaning previous IPSec key exchanges could be decrypted by an attacker if the current one is compromised.