I do like to give advice and help out when I'm browsing around a store, but I also do my best to be careful about only giving advice about products I'm familiar with and giving my best unbiased opinion about anything they ask about. I never interrupt the salespeople on staff though... that's just rude.
I do often end up chatting with the people selling nooks at Barnes & Nobel... the stores around here put pretty technically inclined people by the nooks, so it can be fun to pester them from time to time