I have two tips for you (have more but these two occurs to me now)
1. It is regular visitor's demand that they would like to subscribe to the feed of the latest posts. All you need to do to edit the headinclude model adding this line into it
<link rel="alternate" type="application/rss+xml" title="UKWW latest posts" href="external.php?type=RSS2&lastpost=1" />
2. Robots really like vBulletin so why not ping them when something fresh content added.
You will need this
post pingers mod
I placed this services into the ping list:
rpc.pingomatic.com
blogsearch.google.com/ping
rpc.technorati.com/rpc/ping
api.my.yahoo.com/rss/ping
ping.blo.gs
note: don't forget to exclude the hidden forums, specifying their IDs at the setting page, since i guess they wouldn't like to come to your site for nothing.:-)