Matt Cutts of Google has announced that Google Caffeine has gone live on 1 data center and this has been confirmed by other members of the Google team at PubCon.
Here at AlreadyHosting.com, we enjoy having fun “webmaster related” contests. We are going to give $50 cash (in form of a Paypal payment) to the first person to confirm which data center Caffeine is currently live on and offer support to why they think this. ** Maybe we can get Matt Cutts to confirm our winner ** 
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This is information a lot of webmasters would like to know so this could end up being a very fun post. The only way to win is to post the correct answer (via a comment) on this post. This contest is sponsored by AlreadyHosting.com! Make sure to register for an account (with a valid email) so that we can get a hold of you if you win.
P.S. Matt Cutts you are eligible to win if you would like to enter 
I found two links actually
It is http://66.102.7.18/ and http://216.239.59.103/
November 17th, 2009 at 8:25 am
Google caffeine is is currently unavailable due to maintenance..
some rumors is spreading…
the ip may be
66.102.7.18
or
216.239.59.103
waiting for the release….
November 17th, 2009 at 10:46 am
Get some more updates….(i am not sure about this whether the caffeine will come here..)
216.239.59.81
waiting for the real ip
keep looking @ http://www.webmasterworld.com/google/3985342.htm
and
http://www.mattcutts.com/blog/
November 17th, 2009 at 11:23 am
Well the IP is http://66.102.7.18/ I believe…
November 17th, 2009 at 12:00 pm
As for the reason, search results are different, many have dropped ranks whilst others have risen.
November 17th, 2009 at 12:01 pm
hi,
great idea for the contest, i will try:
http://209.85.225.103/
November 22nd, 2009 at 11:54 pm