There is no quick way to find threads that you took part in but you can watch topics or bookmark posts, or watch topics automatically when you reply to them.
I see. But this way requires user action on each post and does not work on old posts. I could make it the default but that would make the normal usage of watching posts not very useful.
So I hope it would be easy to write a plugin or some other extension which would add the "threads you took part in" link?