Right now, the best way to find content written by a certain user is to search a key word and insert their nick as the author. If you want to find a specific topic, you'd insert the key words you're looking for. If you want to find as many posts as possible you'd insert the most common key words (the, and...).
However, this would require harder work which is also inefficient as you'll never find EVERYTHING this way (especially when there's a minimum of 3 characters key word).

This is a simple idea that exists in many forums: Add an option to see all content of a user through their profile. For convenience sake, divide it into "all threads" and "all messages", basically just like in CFM forums.

would the divisions be something like this or (bad photoshop skills aye)

that's up to the admins ^^