Hi Mark
Right now, I'm focusing on Core, LiquidThreads and the Usability Initiative extensions. If you have an extension that you'd like feedback on, let me know and I'll have a look.
I'd love to get some feedback on the DataTransclusion extension http://www.mediawiki.org/wiki/Extension:DataTransclusion. It lets users fetch data records from pre-defined data sources, and hands the data fields to templates for formatting. I hope that this can soon be used for bibliographic records, census data, etc on wikipedia. It would be great if you could look especially at security and scalability.
thanks daniel