On Fri, 25 Jul 2008 13:45:10 -0700 (PDT), Chris wrote:

Also, am I correct in understanding that
oyster PAYG works for Chiltern Railways in the LT area? I've a US friend
visiting soon, and I was going to lend him one of my oyster cards- and
he's intending to visit Wembley while in London.

Out of luck - they only work on Chiltern where they share an station
with LU.

Not any more - you can now also use PAYG at Wembley Stadium to
Northolt Park (i.e. all Chiltern stations in the Travelcard zones).