I would highly recommend against using this tool, as it is against Facebook's Terms of Service. Robert Scoble was kicked off Facebook in January 2008 for pulling a stunt exactly like this (http://scobleizer.com/2008/01/03/ive-been-kicked-off-of-face...). While his fame and contacts allowed him to get his account reinstated in short order, many of us might not be so fortunate.
So in other words, it downloads the ith friend at time 11*i +/- 1s; an average of one download every 11.5s might just be sufficiently slow to avoid getting banned from Facebook. Obviously, Facebook could look for patterns in their logs that look like the tool (too high a ratio of friend data downloads to other pages, for example, or an unnaturally high goodness of fit to 11s plus uniform variation), but it would probably be quite expensive for them to make such searches too complex, and if an arms race between the autoblockers and the downloaders ensued, the downloaders would have the upper hand because Facebook has the disadvantages of needing to avoid false positives and to deal with the large amount of data they would need to process to do any complex statistical analysis across all access requests.
A few sources cite the median number of Facebook friends at 150 - so even at the relatively slow rate of one friend data download a minute (perhaps with some intervening decoy requests), half of all Facebook users could download all friend data in 2.5 hours. A non-bot user could easily hit Facebook at that rate, and Facebook would get very bad PR if they started banning a significant proportion of their user base due to false positives.
I would highly recommend against using this tool, as it is against Facebook's Terms of Service
I would phrase the facts a little differently. I would say that if you use this tool, FB may choose to discontinue your service, while not making a personal recommendation either way.
Quite honestly, if FB chooses to "kick me off" for taking action to reduce my dependency on their service... No great loss. My business will not fail. My kids will still love me in the morning. And my friends will email me as they always have.
Ultimately, I view the threat of kicking me off FB as roughly equivalent to a cable company telling me that if I don't take a particular bundle of services, they won't do business with me any more. Well, ok, you win, let's not do business any more.
I'd be curious what would happen if thousand of people used the tool rather a lone researcher.
As we saw with Facebook's censorship and uncensorship of lamebook.com, their "terms" seem to be essentially "we'll do what we can get away with and back-off if enough people push back".
Well, if you intend to leave facebook anyway and want a dump of your frendlist to invite them to some other, more open social networking system, it doesn't matter that you get banned does it?
