Do something completely unique. e.g. don't compete with our services

No, in reality, there are already dozens of "forums, link exchange scripts etc.". To make coding an app successful it either needs to be completely unique or you need to add some really cool new features to an already existing concept.

I like the unique approach becasue if the idea takes off then you have the satisfaction of knowing that it was your idea. But, adding cool features is less of a gamble and might be safer.