I once had case where a customer logged a ticket due to a 5800 gateway being unresponsive, CPU's pegged etc. did some troubleshooting and narrowed it down to VPND. Customer of course insisted nothing changed in the environment.
The gateway was the hub in a community with about 100 smaller sites hanging off it. Eventually I managed to run vpn tu and saw there was something like 30 000 tunnels!!! Long story short - one of the customer admins was troubleshooting an IPSEC issue the previous evening and changed the VPN Tunnel sharing setting from "per pair of gateways" to "per pair of hosts" and due to traffic patterns the poor gateways started building tunnels until it almost melted:-)
Think I might still have a screenhot of the VPN TU output kicking around somewhere:-)