I've noticed my per round payout has been getting smaller too! Even after the difficulty change. I also notice that the pool hashrate is getting much faster, which translates to your shares being a smaller % of the total round shares!
Right but at the same time the number of solved blocks per time t goes up so you get paid out a smaller amount more often.
Right, but the difficulty has increased, so now (all things being equal) it will take more work to solve each block. so that will tend to counteract the more frequently, except if ones compute power scales with difficulty... as we are knew it could seem that way for the first few increments in dif... however, relatively, my hashing power is getting smaller.. so the payments will drop in size... and thus i'll make less as difficulty increases. (so will anyone whose compute power is static)
Difficulty increases will keep people who consider it, from going hog wild on new hardware... unless BTC value scales with difficulty... which it won't do in the short term. And I don't know enough about the BTC economy to make any long term predictions whatsoever.