Getting Ready for England

Hi All,
My name is Ryan and I am an American who is about to relocate to London. As sort of a joke Christmas gift (but not really) my folks gave me this book by Toni Summers Hargis -- a very British sounding name, and it contains several chapters on cultural differences as you would imagine. One is on language entirely -- both the small semantic misunderstandings that can easily occur, and the larger social taboos and ignorance between American and British culture. So what have I learned so far?
1) If a Brit leaves the room to go “knock up” another sleeping guest, he is not intending to impregnate that person. Simply wake them
2) Underpants are pants. Outer garment = trousers.
3) The phrase “I’ll be with you momentarily” is likely to cause confusion, since a more literal translation is likely to be taken by the Brit – making the meaning of the statement that the time spent during the actual meeting will be quite brief. I love that one!
Anyone have any other potential language pitfalls they want to share for the hapless American before his departure?