I completely agree with claus on this. You know how I mentioned about site ripping through a proxy - already saw it on a clients site as I'm sure they didn't prefetch over 1200 pages (at 0 seconds between pageviews/pages)... So this morning I am banning it from all sites I have control over instead of just a couple I was concerned with.
As Brett stated it uses your browsers UA so it can't be blocked via UA string.
I think the only way to block it is through the IP range of 220.127.116.11 - 18.104.22.168 via .htaccess . I send them to a custom 403 on another domain (the .net,.info etc of the same domain name) in which I added one of the reasons they may have been blocked was by using the Google's webaccelerator.