I installed the Sitewide tags plugin on my WP 3.0 MU install and then network activated it so that posts from all blogs under this installation would be shown on the Tags blog.
However, when I post on any of the blogs other than the main one, nothing happens on Tags. Only when I post on the main blog are the posts carried over to tags.
That is what appears to be the case to me, however andrea_r has recommended the plugin to me and many others using WP3 and he or she seems to have a great knowledge on WP. So maybe it’s just a matter of changing some code?