Brajesh Singh

This is a plugin for wpmu/wpmu+byddypress powered websites, where network administrators can limit the number of blogs a user can signup. 
It is pretty simple and adds an option to NetworkAdmin->Dashboard->network settings page, where you can limit the number of blogs. No additional frills required.
What It does
It adds an option to the Network settings page when you are logged in as site admin of the wpmu site(or wpmu+buddyppress site),Look at the bottom of options page,and You will see a text box like this asking for number of blogs allowed per user.If you set it to zero(which is the default),It will not restrict the blog registration then. 
For any support or any questions,please leave a comment at my blog
<a href="http://buddydev.com/buddypress/limit-blogs-per-user-plugin-for-wpmu/" rel="nofollow ugc">http://buddydev.com/buddypress/limit-blogs-per-user-plugin-for-wpmu/</a> 
And yeh did I mention <a href="http://blog.strategy11.com/" rel="nofollow ugc">Steph</a> has been very kind in reporting bugs and suggesting fixes.Many Thanks to Steph.

Limit Blogs Per User

This plugin is for WordPress Multisite and/or WordPress Multisite+buddypress based social network.It limits the number of blogs a user can create.

Joshua Parker

If you are running a WPMS (Multisite) blogging network, the issue with most login widgets that you add to the main site’s sidebar is that it doesn’t pull the user’s own blog info. That is why the WPMS Sidebar Login Widget was created. Instead of the user trying to remember the login page of their own site/blog, when a user logs into your main site, the widget will conveniently contain links to navigate to 3 different pages of the user’s blog: dashboard, new post page, and profile page.
Features:
<ul>
<li>Link to Network Admin page (only shows if user logged in is a super admin)</li>
<li>Link to user’s dashboard</li>
<li>Link to user’s new post page</li>
<li>Link to user’s profile page</li>
<li>Link to forums page</li>
<li>Subblog registration detection</li>
<li>Custom CSS settings</li>
</ul>
To make sure it works, activate the <a href="https://wordpress.org/extend/plugins/user-switching/" rel="ugc">User Switching</a> plugin on the main site only to switch to a different user.

WPMS Sidebar Login Widget

Adds a sidebar widget to the main site of a WPMU/WPMS install.

Limit Blogs Per User vs WPMS Sidebar Login Widget