Users
openSUSE
The openSUSE project uses the MirrorBrain on download.opensuse.org. This is where it was developed.
The file tree is about a Terabyte in size, and contains more than 700.000 files. The box running the MirrorBrain gets 20.000.000 to 40.000.000 hits a day. The mirror database knows about 100 active mirrors.
Go-oo
The Go-oo (OpenOffice Development) project uses a MirrorBrain, which can be found at http://go-oo.mirrorbrain.org.
Tree size: 5G, ~1000 files. 13 active mirrors in the database.
Users in spe...
A few days ago (end of August 08) I have set up a mirrorbrain instance for the Samba project at http://samba.mirrorbrain.org/, for them to evaluate. I hope they will consider it as their mirror system.
Another, bigger setup (88 mirrors!) is for OpenOffice.org (http://openoffice.mirrorbrain.org/), for the purpose of evaluation.