Unlimited Users on Private Blogs
This upgrade will be of use to those of you creating a community around your private blog. It removes the 35 user limit on private blogs so you can invite as many people as you like.
The free limit of 35 users will be enough for most people but if you’re building a private site that will have a large community or you’re a large organisation buying this upgrade is the way to go.
Simply login and go to your Upgrades page where it can be purchased for $30/year. Now, when you go to Options -> Privacy it will look like this: