I will probably renew my subscription at some point to help the site, but I will admit I am in no rush to do so.
Here are my thoughts:
1) Subscriber only stuff: I have taken a look at it from time to time but I have never seen anything I was particularly excited about. I mean the amount of content is well worth the small price, but there's nothing there I'm that into.
Part of that my also be that I honestly couldn't tell you what content I have as a subscriber. Is there a singular place somewhere that has a list of all the good stuff I get? Is there a place for a non-subscriber to see the list of goodies he would get by subscribing?
Lastly I had though that the search function would be the number 1 thing I would like being a subscriber. I did use the search function from time to time but not nearly as much as I thought I would have.
2) Changes in the forum as a whole. It may be the forum reorganization as Morrus said, but to me the perception is the site has slowed down quite a bit the last few years. There are three forums I visit religiously...General, 4e, House Rules. I browse pathfinder once in a while.
I never really look at the other forums and personally don't like a lot of different forums. I like a general forum that is hopping with new content all the time, it lets me get a peak into threads I might never have noticed because they were in a smaller forum.
3) What I want. Right now, what do I want out of being a member? My main answer is speed. Features are nice, but at the end of the day I don't have a lot of free time anymore. I want to go to my 3 forums, see new content, write some posts, and be done.
The boards performance has been good ever since the last big sql cleaning, but if membership gave me preferred speed rates, extra features that made my browsing quicker, etc then I'd pay you more than $3 a month. Time is money afterall.