General search is still valuable for finding random programming examples that don't appear on Stack Overflow - there are a lot of blogs that usually have some helpful example.

For FB if there was something that allowed event planning, but didn't require people to create accounts for it (basically event planning with RSVPs, but handled through email or text).

It'd be nice if this extended to optional accounts that had up to date contact information - this is the main thing I'd worry about missing (though I think Apple could just implement this by optionally pushing changes to the people in your phone with your contact information when it changes).

For Twitter - there's a lot of value if you curate people you're interested in and engage with their tweets. People you would otherwise have no access to and interesting discussions/links/discovery happen there.

Twitter can be great, but requires some effort. I think this would be helped by 'index lists' of users that are interesting to follow for new people (though this would cause a similar bubble issue that financial indexes have) but at the moment looking at someone you find interesting for who they follow is a decent way to find people.