Hi,
I developed a C# plugin called Invisible Lists. It allows you to create different groups of contacts (different from the ones you have in your contact's list) and to block/unblock them. It can be useful when you're at work for example.
This is an alpha version which means that it may have some bugs
To install just run the exe file in the attachment. The plugin has an help section accessible through the Plus!>Preferences>Plugins>InvisibleLists>Configure... (that's also where you configure your groups and other options).
Since this is a C# plugin, if you have another C# plugin installed in plus then you'll only be able to see one of the plugins in Plus! plugins' section.
Any comment/suggestion/bug, just post here or write me an email.
Update: Sorry, the plugin had some annoying debug messages (all removed). Thanks to J-Thread for letting me know.
Enjoy,
Ricardo Sabino.