That's what drove me away from DP and similarly what drove me away from WTF. That is why NB is so awesome (from my pov).
That idea could work.
Another idea would be to leave it as it is, but highlight each thread into those three categories you mentioned e.g. red for GC, green for webmaster, blue for marketplace *see attachment for what it would look like. Reason: because even though someone only wants to post in GC, they may see a marketplace sale that they are interested in or a marketplace discussion that they want to participate in (i.e. stimulating conversation)
With the highlight method, it is sooo easy to e.g. look at only GC (just looking at the red forums) or webmaster (just look at green). Seriously, try it in the attachment. It also eliminated the need for 4 different lists. We need to keep things simple here and to me this is the simplest (and just as effective) way of splitting up new posts.
The highlighting idea could also be applied in the new posts in 'user cp' and 'todays posts' and you could make an option to turn the feature off if people find it annoying.
This idea could possibly work also but it sounds pretty complicated. Think we should try one of the above options before doing this
Yum, what did you have? :D
We need to stop this happening in NB when it becomes massive :)
I agree, GC is a place to relax and we cannot expect members to post massive and complicated posts. Therefore, short and to-the-point posts are acceptable. However the webmaster forums should be very strictly moderated because that is the real place people look for quality in a wm forum.

