You can now post new messages through the PC.
You can also follow people now from the PC.
Originally Posted by JSR
The update looks to be pretty substantial beyond just posting from the web. You can now also follow people from the web app, as well as view friends/following lists, update profile details, and edit general Miiverse settings (i.e. who can comment on your posts). All that's left to add seems to be Private Messaging.
(You now can) View any Miiverse post, even if you don't have a Nintendo Network ID or are not signed in. As long as you have the URL for a post, you can open it.
Originally Posted by GRW810
The restriction between making new posts has been reduced from five minutes to three.