This is a really, really good idea. Much time has been spent discussing separating different parts of your social life, but the idea of doing it based on "shared secrets" is great.
A big obstacle in my mind is duplication of overlaps, e.g. 'I read Hacker News' and 'I read HN'. The both mean the same thing, but if two users click "Me Too" on the different versions, they won't see the common interest. People may be tempted to just add a new overlap instead of searching for an existing version, especially as the number of users and possible overlaps grow. Hopefully you can find a way to have the community help aggregate overlaps.
I would recommend a user curated feature to that marks 'overlaps' as duplicates that then get sent to some human to moderate. Similar to user curated spam or inappropriate material.
A big obstacle in my mind is duplication of overlaps, e.g. 'I read Hacker News' and 'I read HN'. The both mean the same thing, but if two users click "Me Too" on the different versions, they won't see the common interest. People may be tempted to just add a new overlap instead of searching for an existing version, especially as the number of users and possible overlaps grow. Hopefully you can find a way to have the community help aggregate overlaps.