I live in central Jersey...
No one in Jersey says 'Joisey'. Doesn't exist.
Near Philly, people have a similar accent, with things like 'awn' (on) and 'cawfee' (coffee).
For me, I have a neutral accent from a mix of New York and Philly... and interesting Jersey thing is actually changing 't' and 'd' before 'r' into 'ch' and 'j'. So I say 'chrue' (true) and 'jrawer' (drawer).
Up north, there are tons of different accents, some affected by NY more, and some less.
I plan to do a dialect study soon... =] I'm a linguistics minor.
(For reference to other Jerseyans, I'm from Ocean county)