Thank you everyone for all the information. Some great tips!
After looking at the various aircraft rental companies it seems that they
expect you to take out a minimum amount of hours/day when taking the
aircraft on a multi-day trip. Is this negotiable when taking the aircraft for
longer term, say 2-3 weeks?
Not sure, but try your luck with various outfits. It also depends a lot (in my experience) on the type of a/c you rent. If you go for one of the popular trainers, then not likely, some of the more expensive/complex types which don't get rented out all that much, possible. Ask.
Also, some of these companies mention a "renters insurance", is this
something I will need to arrange myself or will it be included in the hourly
rental price?
No, this is something you will have to arrange. The two biggest outfits doing this are AOPA (US) and AVEMCO. You will need to provide a US mailing address in both cases (can be a friend's place). This can be done over the phone and cover is instantaneous. Discuss with the rental outfit what level of cover you need; this varies according to the hull insurance they have.
What can I expect when having to do a pre-rental check-flight? Would you
recommend a few hours flying with an instructor to get used to flying
Stateside? What are major differences when comparing JAA vs FAA? Is there
a way of preparing on forehand with differences in procedures?
Basically, a BFR and yes (especially if flying in highly congested airspace like L.A.) a couple of dual hours are probably a good idea. If you've never flown in the US, then I'd suggest buying a couple of US charts (get a sectional and a terminal area one) and the Guide to the Flight Review, an ASA publication and read up. Both are available from the usual suspects (pilot shops) in the UK.
How long would it take to get used to an aircraft equipped with Garmin
G1000? I understand some flying school have a special short groundschool
on this. Is it worth the hassle or should we stick to an old-fashioned steam
gauge Cessna? Does it help to have jet EFIS experience?
Alas, I'm somewhat lacking in both jet EFIS experience
and G1000, so cannot really comment. From what I've heard from pilots transitioning from steam gauges to glass, the difference is significant. If you're used to Cessna steam, then I'd probably stick with it.
Would anyone have any recommendations on any good places to see in the
Pacific Northwest?
Pass, but watch the wx up there !