scribu

AppThemes

With the current WordPress administration area, the only way to add existing users to a certain blog is by entering their usernames, one by one. It’s very time consuming.
With this plugin, you can do it in bulk, by using the familiar “Change role to…” dropdown:
<ol>
<li>Go to WP Admin -> Users.</li>
<li>Click the “Entire Network” link.</li>
<li>Check the users you want to add.</li>
<li>Choose the new role from the dropdown.</li>
<li>Press “Change”.</li>
</ol>
Note that you have to be a super-admin to be able to do this.

User Management Tools

Allows super-admins to quickly add users to a particular blog in a multisite installation.

Sam Margulies

Ever have one erroneously entered custom field name confuse all of your users and you just can’t figure out how to get rid of it? Delete Custom Fields will let you delete every instance of a custom field from your site. Once your remove a custom field using this plugin it will not appear in your list of custom fields when you edit a post or page.

Delete Custom Fields

Doesn't show all custom fields, though (even if you choose Show Hidden) - would be nice to have them as a list instead of a dropdown, but otherwise it does what it promises.

Works

Remove every instance of a custom field from your site.

User Management Tools vs Delete Custom Fields