crossing the adriatic

[Five Horizons]

Howdy,
This summer (early June to mid/late August) I am going to be backpacking through Europe. I was wondering if anyone has any advice for dealing with the ferries from Bari, Brindisi or Ancona, Italy to Patras, Greece or the crossings between Bari, Italy and Dubrovnik, Croatia. Basically, I'm wondering if ferries are the way to go, in terms of price, time, convience etc. I will have a Euraiol pass so I know my crossing from Italy to Greece and back is covered. Also, I was wondering if it would be worth is to cross the Adriatic again after that to explore Croatia (split, dubrovnik, hvar, korcula). Oh, and one final question: do I need to make reservations for these ferries and, if so, how far in advance?

Thanks
James