Hi Andreas,
More seriously, we really don't have any stats for ftp.squeak.org?
I have squeakvm.org logs going back 12 months, during which time there were 30,000 downloads of .tar.gz archives from the site. I'm not sure offhand what proportion of them were due to search bots or how many unique IPs were involved. I can count the .zips for you, if you like, or just look in /var/log/apache2 for yourself.
If squeak.org runs on apache and uses logrotate to manage /var/log then there should be 12 months of download information from there too. The programs "webalizer" and "analog" make it easy to extract the information you're after from the access.log.* files.
There are also installations via the several Linux distributions that offer the Unix version of Squeak. I can't think of any way to estimate the stats for those. Plus, thanks to Bert et al, Squeak shipped with the OLPC. I can't think of any way to know how many OLPC users should be added to the total.
(BTW: having access to download statistic is another reason I'm not fond of 'third-party' hosting.)
Cheers, Ian