well from the starting line up, seedorf retired, van bommel is going back to psv, and nesta retired, which is a pretty big blow considering the experience they brought to the team. plus if you consider pato's ongoing fitness problems, milan may very well be very active this off season, and it will be very interesting to see what they do.
juve won the scudetto and will be looking for a strong performance in next years cl. however i doubt they can get all that far again on defense alone, and will probably be in the market for a striker. so far ive heard rumors that they are very interested in Higuain and as you said, im sure they will be at least thinking about cavani or lavezzi.
i agree with what you said about napoli, and i am somewhat concerned because they are one of my favorite teams. it sucks that they just missed out on CL qualification because now I could see lavezzi or cavani being more open to leaving, specially if its for a team in CL contention, like juve.
and as usual, it is always interesting to see what barcelona does. despite villa expected to be fully fit by the start of next season, i could see them investing in a striker anyway to help messi out with the goalscoring duties. maybe a bigger guy that can get some headers and keep the defense honest. also, as im sure youve heard Puyol is out again and will miss copa del rey and the Euros and will be undergoing surgery. Considering that he is already in his 30s and piques form is declining, i wouldn't be surprised if they made some ridiculous offer for Thiago Silva.