I agree with the 3 month idea....it`s alright joining a forum, taking what you need from it and then doing nothing by way of any acknowledgement but that`s not cricket old chaps!!
A lot of other forum`s insist that a certain number of posts in a set period be made or you are forced to re-join or access to certain areas only.
I know you can`t make people post with a reply but let`s play the game peeps.