You can now update Wikipedia using rsync.
Get directory wiki-xx/ from tarball
or create empty one and then:
rsync -rz wikipedia.com::xx/ wiki-xx/
Because rsync works in real time (unlike daily tarballs)
and transfers only what actually changed,
now it's quite reasonable to have mirror of wikipedia that's
updated by cron every hour or even more often without using any
extraordinary bandwidth.
Only pl, de and eo wikipedias are available now.