Dont ask any Bostonians to say "Park your car in Harvard Yard" My mom is a REAL Bostonian, grew up in Irish Dorchester, and she has a real Boston accent, and while listening to it can be a both amusing and befuddling, Bostonians are a very proud people, as they should be! Some of the best people on earth here! They dont like to be teased about their accent!
While in Boston keep in mind that they speak with a New England accent. If a word ends in an 'ER', pronounce it like it ends with an 'AH'. If a word ends in an 'A', pronounce it like it ends in an 'ER'. For example, Marina is 'Mariner' and Jennifer is 'Jennifah'.
Many people talk in the famous Boston accent. I'm only really qualified to talk on a few intricacies of this dialect, but Adam Gaffin has compiled the excellent Wicked Good Guide to Boston English at Boston-Online.com.
Just one more thing. Never refer to Boston as Bean Town. Just as no San Franciscan refers to their city as 'Frisco', we prefer not to refer to Boston with a nickname featuring brown ovular objects. Feel free to do as us locals do and call Boston 'The Hub of the Universe' or just simply 'The Hub'.
I'm a transplant to Boston, so learn from my mistakes--there's some bizarre nomenclature here. The lowdown:
1) If you order a milkshake, they'll give you milk mixed with flavored syrup.
2) If you want what is called a "milkshake" in the rest of the civized world, order a "frappe."
3) But you have to pronounce it "frap."