For anyone wondering about difficulty in regards to pool mining the ideal difficulty allows you to get at the very least 1 share per block so you are rewarded for your mining.  In my opinion you should target your difficulty so that you are consistently submitting multiple shares in a 2 minute period since the target block time is 2 minutes.  If you target your difficulty too high you might not submit any shares during the mining of a block and therefore not be rewarded at all.  On the other hand if you set your difficulty too low you will waste time getting new work.  It is best to find a good medium that allows you to utilize your computational power appropriately.  I have my pool set to adjust difficulty for miners and automatically targets having each miner submit a share every 20 seconds. This should allow roughly 6 shares every block and in my opinion allows miners to be rewarded accurately for their mining.  Hope this helps those wanting to set their difficulty manually.