Speaking as someone who moved here a week ago:

1. Haven't had culture shock yet - but sticker shock has definitly set
in.  I forgot how much little stuff you need to set up life - and
we've yet to spend less then 100 bucks on food and our fridge is 3/4
empty.

2. If you want a bed larger then a twin/full bring sheets (we've been
all over town and haven't found anyone who sells queen sized sheets). 
I'm going to see if I can find some in Tokyo next week - any advice
would be appreciated - otherwise it's going to be continuing to use 2
twin top sheets for our bed until I can wrangle a trip back to the US.

3. Bring a good number of travelors checks since banks here won't take
US personal checks even with a long wait for them to clear (CitiBank
wouldn't accept 'em anyway).  Not a huge problem since everywhere
takes Visa and most ATM's are on PLUS so your ATM card should work. 
Try to set up a bank account that will let you do internet transfers
before you leave and maybe set up a CitiBank multi-money account while
your there.

4. The hardest part of driving (for me) wasn't remembering which side
of the road to drive on, it was the fact that my spacing is WAY off. 
Getting used to having no space on your right side and needing space
for the car on the left is rough for me.  So far I haven't hit
anything other then bushes but I'm waiting for me to scrape someone.