If you are looking at a post, you have the option to "Send as email" which gives you the option to select users that are online, newest, or browse directory.
I agree, it would make sense to add a "My Connections/Friends" tab to the User Picker. I've gone ahead and filed an enchancement request for this: CS-12678
To better serve our customers we have included functionality to automatically follow up on a case after it has been idle for more than 5 days, and then auto close after an additional 3 days of inactivity. Choose No to acknowledge that this case will remain idle for longer than 5 days.
Making cases public allows other customers to learn from the solution of the case. It can also be used to gain feedback from others in the community. Ask our Support Engineers for more info, but we encourage you to make your cases public.