WordPress MU

These plugins are really needed for a blog hosting site. Hope developers of plugins can come out with these plugins.

1. Sitewide whosonline.
2. Sitewide most viewed blogs (I am sure members would love to know if their blog is popular or not).
3. Sitewide most viewed post of the day (month).

You should have searched a little :)

1. I guess this: http://premium.wpmudev.org/project/user-activity

2. I think this one: http://premium.wpmudev.org/project/blog-activity
Here're a few alternatives, but I'm not sure if they work:
http://wpmudevorg.wordpress.com/project/most-active-blogs
http://wpmudevorg.wordpress.com/project/Sitewide-Multi-Widget

3. Don't know if this still does the trick: http://wpmudevorg.wordpress.com/project/WP-PostRatings-MU

3: There's a couple of different solutions, depending on how you want to attack it. But as VM mentions, all the poster has to do is search for the previous discussions on the methods involved.

edit: We're running a custom install of wp-shortstat with a script that runs through every hour, grabs the necessary data from posts within the last week or so, compiles a separate table, and pulls it from there, depending on what's needed.