We have been to PI twice this summer. Not really much of a difference other than the first club you enter, checks your ticket and gives you a wristband. As for the alcohol - you can take it from one club to another (just like always) they just don't allow glass bottles so they have plastic cups for you to pour your beverage into.
The only real difference that I saw was the amount of parents there with their children. Many strollers in the street, etc. I realize that Disney is family oriented, but we saw many adults tripping on the strollers (and not because they were intoxicated). I know I will get "flamed" for complaining about people bringing young children, but we just never considered taking our children in strollers to a party atmosphere and staying until midnight. All that being said - the clubs seemed about the same, just the street that was different!