Internal Host Caches (gnutella.net files) do not expire after a week, they still work even months after the last use. they even work better now, 'cause most of the stored ips are ultrapeers which have a longer uptime than regular gnutella nodes. i don't remember the exact numbers, but some guy on the GDF once proved mathematically that with 1,000 stored IPs you have about a 90% chance to connect even after a year, and a 97% chance with 10,000 stored IPs...well, i'm not sure how accurate these numbers are, it's been a long time ago, but yet you have a very good chance to connect without central pong caches...