If you haven't tried it yet, please give the release candidate a try:
http://download.wikimedia.org/mediawiki/1.18/mediawiki-1.18.0rc1.tar.gz
If you've tried it out and found a problem, please let us know.
But, if it works for you, please let us know that, too.
For example, I upgraded a MediaWiki site that I maintain from 1.15 to
1.18. Except for some trouble with the customized skin, things went
smoothly.
I added my report to
https://www.mediawiki.org/wiki/MediaWiki_roadmap/1.18/Installation_reports
but it is looking pretty lonely right now. Please add your own
experience.
Thanks,
Mark.