It’s officially out: WPMU 2.9.1. As Donncha says, this will likely be the last release before 3.0 and the merge.
PLEASE see the info about adding the new commentsmeta table.
(Wow, what a crazy ride. 
)
2.9.1 released, last before merge
January 14, 2010 By
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So if we hold off on upgrading until 3.0, will the commentsdata add process still be necessary?
Donncha is suggesting to add it this way, in case it fails during the upgrade process.
Gotcha, I better go re read his original notes on this.
I updated my 2.8 version to 2.9 and then noticed that the mu-plugins is no longer being used.. I use the “userthemes” plugin which is installed in the mu-plugins folder.. anyway around this? or do I just have to go backwards?
What do you mean by “not being used”? Because it is definitely still supported, and was already in single WP months ago.
On the other hand, I have seen posts from people having issues with the userthemes plugin.
For me to get it to work I had to move the “userthemes” php file from the mu-plugins folder to the regular plugins folder.. cleared it right up.. but that’s just me.