GD, and in fact the whole of the forums to an extent, tends to go in cycles which although it sounds a bit trite seems to be true - plus ca change, plus la meme chose. Just thinking about the time of year it may also be with the resumption of university that the quality improves again (whether that is because more students or less will post I really couldn't say).
However every so often in the cycles it seems that things work themselves up or down to a level and then the pendulum tends to swing back the other way so depending on whether you are a positive or negative person - if it's at a point you like then we're probably less than 6 months away from a dip, if it is at a point you don't like we're probably less than 6 months away from a peak.
I do reckon that there are still some quality posters around but not everyone maintains the same level of interest throughout so you might see less of them from time to time.