Taken from: The WordPress MU Manual
WPMU default setting for plugins is disabled. If you want users to be able to access regular plugins you first need to enable them site wide.
1. Click on Options (Site Admin > Options)
2. Select Enabled for Plugins
3. Click Update Options

Activating and deactivating regular plugins sitewide
There are two options for regular plugins:
1. Activate Plugin Site Wide –activates the plugin site wide i.e. plugin s automatically enabled on all blogs on the site and users can’t deactivate it

2. Activate Plugin Per Blog Basis – allows users to decide which plugins they want to use on their blog i.e. users can choose which plugins they want to activate/deactivate






I have one wpmu install for multi-site/domain
So site activation is running per domain ?
I am not sure if this is the right page to post this but I am looking for a plugin that would do the following:
1) whenever my blog post gets published, the plugin automatically posts the url of the post to social media and social bookmarking sites I have preprogrammed in (with logins/passwords)
2) After it’s posted to the social media sites, it then creates a forum thread on some forums I’ve preselected and entered login info for.
Is this possible? Please email me at the email I’ve supplied for this post.
Thank you in advance. NOTE: I’ll PAY for this custom plugin, not looking for a free solution.
I reckon you’ll be best off here asking for that :)
http://premium.wpmudev.org/wpmu-jobs/