PIC, the ability to IM between OCS/Lync with AOL, MSN/Hotmail/Live and Yahoo! is a great feature but during December each year any problem customers face hit one additional hurdle – Datacenter Lockdowns.
The purpose of a lockdown is to bring stability for business or holiday reasons, which means folks take vacation. Here in lies a difficulty for PIC issues as the likelihood a key contact is needed they may be out.
And while this post is old, not much has changed in the world of PIC so it remains a good reference - http://blogs.technet.com/b/toml/archive/2005/12/30/lcs-pic-troubleshooting.aspx