Just for the record, I have successfully installed Update 2 on two SME boxes that compose an IPSec VPN with no interruption to said VPN.  Not that the update SHOULD'VE broken anything, but I was concerned.  I should also note that I was participating in the WAN via PPTP login and was able to update both servers during one session.  Again, that's how it's supposed to work -- I'm simply reporting success in case anyone else was concerned about implementing this update.  Standard disclaimer:  YMMV.