Sand - 3:21 am on Jun 14, 2012 (gmt 0) [edited by: Sand at 3:22 am (utc) on Jun 14, 2012]
The other scenarios you mention are also quite natural and not a problem.
A thousand times this. People who talk about similar topics link to each other. That's how the internet works, and one of the reasons it's so great.
Just keep your reciprocal links on topic and relevant. Adding a reciprocal link to that spam directory in exchange for a free listing isn't going to anyone any good. Neither is having a partnership with an off-topic site.
It's probably not worth your time to actively seek out reciprocal links, though, unless they're actual traffic drivers in their own right. Whether they work or not is irrelevant -- they very well may. But there are many other ways you could be making use of your time.
[edited by: Sand at 3:22 am (utc) on Jun 14, 2012]