Yahoo Answers is another good source, which more or less acts like a forum. Why do I recommend Yahoo Answers, when we have forums? It’s not because its another source.
It’s because Yahoo Answers is different
When you are in a niche that has a popular forum (like WarriorForum, and programming related forums), most of the people hang out in the forums. These guys know all the “forum stuff”, and their attitude is more or less predictable.
But did you ever think of joining Yahoo Answers when you were just starting out in your niche yourself? Why? Did you find it childish?
The fact is, you will find a slightly different crowd in Answers. You will be exposed to new possible queries and problems people are having. A quick glance at Answers can give you the entire story about the “current trend” in the niche.
This information is only a search result away. Enter the niche keywords in Answers, set date of question to something like a month (or even 7 days). This will give you the current “trend” of questions in the niche.
Also, one good thing about Answers is that one account gives you access to practically all niches. No maintaining different accounts for “each forum”.
But I highly recommend using all idea sources. What one may contain, another may not.