I have been playing some 5NL and some 10NL. For some reason I noticed there are way more fishy players at the 10NL. A lot more action going on.
I found at 5NL people are very scared to put money into the pot, and when they do they just have it. At 10NL I found there are regs and fish, and not much in between.
Another reason I am thinking is there are a lot of serious players at 5NL who are learning, but are learning seriously, and therefore at least have a pretty good clue.
I play on ipoker.