the fast ferry takes 2 hours, the normal ferry takes 4. the fast is about 30 to 40 % more expensive than the normal one (depending on which company you use - balearia or iscomar)
depending on the time of year and day there are sun loungers on the decks - just like being on a mediterranean cruise. there are bars, cafes, a tv lounge etc. it's not like being trapped on a plane with nothing to do and of course you don't have to check in hours before!
i use the ferry to take my car over to the mainland on long holidays and i use the fast ferry for weekend jaunts
eg leave ibz 8pm friday arrive palma 10pm
leave palma 8am monday arrive ibz 10am
less than €50 (with my third off residents discount)