I think that the overall quality of HN posts has held up very well given the growth in the community size. OK - some of the stuff that I find interesting and which might have got a bigger feature a couple of years back can tend to drop out of view a bit quickly under posts about "pop" tech companies but they are still here and findable.

I am currently working on a "specialised" social bookmarking site and have gone with only up-votes (posts and comments)and a facility for flagging spam or the inappropriate. I am confident that this simple approach will share some of HN's benefits.