I've always been a big fan of secure Exchange RPC publishing. It's been a rocky ride for this protocol, because the Blaster worm gave the RPC endpoint mapper port TCP 135 a bad name and many ISPs just shut down this port, without realizing that ISA Firewalls provided complete protection against Blaster and many other RPC exploits. Then RPC/HTTP became available with Outlook 2003 and that pretty much put Secure Exchange RPC publishing on the back burner.
Nevertheless, many companies can't use RPC/HTTP and still require Secure Exchange RPC. If that's you, and you're using Exchange 2007, you might want to be aware of a problem with the KB925403 update for publishing Exchange 2007 with ISA 2006. This update might break your Secure Exchange RPC publishing.
The ISA Team Blog has a discussion on this problem and a solution. It's worth checking out. Find it at http://blogs.technet.com/isablog/archive/2007/12/12/publishing-exchange-2007-may-fail-after-installing-the-update-update-for-publishing-microsoft-exchange-server-2007-for-isa-server-2006.aspx