Today, for the first time I had more than half of my traffic coming from this Google data center. Is it PR update activity or ? Cheers
No, it just means your site is getting indexed / or checked for new content. The PR update thing just means that (when they do that) they export the internal PR in their database out to the google toolbar.
so what is the problem? this is a good think for you. G has found you and will index your web site. you must be happy