The 1.3 version of Simple Tags says it's compatible with WPMU without editing. I don't see how this is possible, because simple-tags.php needs to be run from within the /simple-tags directory. Plugins to be activated in the /mu-plugins directory need to be in the root of that directory or they don't work.
Amaury noted he was working on some fixes for today. Maybe put a comment with your observation at http://www.herewithme.fr/wordpress-plugins/simple-tags
I wonder if there's any news on simple tags with wpmu - i couldn't find amaury's statement on the link you provided, michael.
ahh good but how? The Problem from post 1 hasn't changed anyhow, has it?