Highlight common friends in profile view, just like common interests.
Short, concise description of the idea
[ see above, it should be enough ]
Full description of the idea
Pretty self-explanatory, but I think it would be neat if you could highlight common friends shared between yourself and the person's profile you're viewing, just like is already done with common interests.
An ordered list of benefits
1. Makes it easy to scan a large "Friends" list for shared friends
2. Mmm, yep. 3 cheers for laziness.
An ordered list of problems/issues involved
I can't really think of any. I'd imagine you could reuse some of the code from the interests highlighting, but I haven't investigated this...
An organized list, or a few short paragraphs detailing suggestions for implementation
I'll leave that to the experts. Aside from possibly being able to reuse some interests highlighting code, I can't think of anything I could suggest that would be at all helpful.