Ok, I have an interesting quesion.
Because the 40x4 LCD has 2 HD44780 controllers, can't it theoretically have 16 custom characters, just 8 in each half of the screen?
Not sure of the possible practical uses of this, just thought i'd throw it out there... 
Mowcius
It looks that way to me. We'll have to get jrraines, the resident 40x4 tinkerer, to verify.
Don
Yeah I am hoping he will see this 
I will send him a nudge 
Annoyingly I am pretty sure that the 40x4 is classed as 2 40x2s top and bottom... It would have been nice if they were classed as 2 20x4s, left and right. Then I might have found a use for this... As it is, I think it's pretty useless but interesting...
Would mean that I could do a 2 line bargraph visualiser on the bottom and custom characters on the top though
Mowcius
sorry I was slow to find this post. I answered the question elsewhere:
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1264823411/105
Yeah no worries, I saw the other post.
I have not tried your proposed code but it looks like it will work. My 40x4 was being a pain last time I used it so I left it for a bit and moved onto removing outliers from my ultrasonic range finder code.
Mowcius