Are all links worth it?
Opinions differ about this question.
Overall, almost all links, even those coming from unpopular pages seem to play a positive role even if it is sometimes a minimal role.
Whether it is dark directories, comments from unknown blogs or simple Web 2.0 profile pages, Google's algorithms always seem to be responsive to quantity.
However, the idea is not here to encourage you to get low quality links...
Can links penalize a website?
In general, Google's policy rather focus on penalizing bad quality websites and destroy the popularity they can broadcast. Why? It would be way too easy to make some links pointing on your competitors websites and thus unfairly getting them penalized.
It is better to focus your netlinking on qualitative links, i.e. links coming from websites indexed by Google (this is the basis) but above all authoritative in their field and in topics close to yours.
Example: You're selling ties online and your cousin who manages a burger restaurant makes a link from his website to yours. This link will probably not be considered as positive or negative and theoretically, it should not bring you any bonus (or traffic).
However, some tests have shown that it is still possible to get great results through links out of topics and very few qualitative, sometimes.
