The BFR isn't that bad, basically, as has been said, its a one hour ground followed by one hour in the air and it's about whether you are safe to be in the air and flying one of the club aircraft. You can expect for sure, questions about US airspace and in particular that you understand class Bravo, Charlie, Delta, Military Operations areas and Restricted airspaces and the clearances necessary to enter them. Airspaces and sectional maps are very different from the UK. You will certainly get questions about aircraft weight and balance and be expected to do a calculation for departure from a high altitude airport because there are lots of them in SoCal. You will have the benefit of the POH so that you can look at the tables and Mr Piper's words of wisdom. You will get questions about runway and taxiway markings and make sure that you know what US road markings look like so that you can differentiate between taxiways and perimeter roads! ALL runway and taxiway instructions MUST be read back on controlled airfields! As I've said before, don't be too sad if you are required to do more than the minimum 1 hr checkout before they set you loose. I trained in the US but I do know of foreigners (yes that's us!) who have been required to undergo more than 1 hours familiarisation training. US traffic paterns might be as odd to you as "standard overhead joins" in the UK were to me.
Have a look at this link, might be interesting to you!
http://www.aopa.org/asf/publications/piper_cherokee.pdf