You use it when you reach level 99 to do the job 'Drug Smuggling at Sea'.
You must buy it from inventory - $400,000
Its only for increasing your attack and defence.
I Think its just For Doing some jobs in New York :D
What it does is you buy it and you can use it when your level 99 so my best bet is to sell it instead of wasting your money personally im level 344 in mafia wars on myspace
The purpose of it is to do the job Drug Smuggling at sea when you reach level 99
Speedboat is NOT a Job item loot drop..you buy it. Check Vehicles page
There are few ways a person can speed level in Mafia Wars. These include logging into the game frequently and choosing the maniac character.
(22.09.09) Part of the Job requirement (1 unit). Dispose of a Body under Consigliere (Lvls 35-59)
you havev t be a shrodenhixer(update 20.09.09) Not sure what is the exact level, but the next level update after you can purchase the town car.
make a Maniac
The speed depends on your internet connection. If you have a high speed internet connection then you can play mafia wars at a high speed.
No, there is no jail in Mafia Wars.