I tried asking these questions in my blog but didn’t get a response there coz I guess admins didn’t see it, hence this thread:
1: How come some private blogs are marked with a “key” and others aren’t? Is there an option that lets you do that or what? I’ve mistaken many private blogs to be public because I didn’t see a key sign beside them … it was only when someone pointed out to me that the blogs were private that I noticed some tiny text beside the blog saying “this is a private blog” … 
2: Can I restrict access of some of my contacts to my blogs?
3: I’m sure there is a technical reason behind the “mention” function not being enabled in blogs but I’m just wondering whether people would like to have it working in blogs too? 
probably not needed, is it?
Cheers!