In case anyone else is banging their head against this:
Some apps now have icons called 
icon@2x~ipad.png. Some of those icons are at 148x152 and some aren't. Some have icons called 
Icon-72.png, some 
Icon-72@2x.png, some 
Icon@2x.png and some use a lower-case 
i and some don't and some don't care. Some have none of those but have icons called specific names. I guess you can go and look in 
/Applications/<appname> to find out exactly.
On a Mac you can use 
pngcrush to 'un-optimize' the native iPad/iPhone PNGs (if you have the iPhone dev kit installed) and you can use 
sips to resize a PNG (the advantage for me over using a GUI is that I could write a script to resize and rename a bunch of icons at the same time).
This is how to un-optimize a PNG:
	
	
	
		Code:
	
	
		/Developer/Platforms/iPhoneOS.platform/Developer/usr/bin/pngcrush -revert-iphone-optimizations -q <input file> <output file>
	 
 
This is a script that resize all PNGs with 
@2x in the name in the current directory and all its subdirectories and to 148x152 and appends 
~ipad.png to the new file name:
	
	
	
		Code:
	
	
		#!/bin/bash
cwd=`pwd`
for i in `find . -name "*@2x*.png"`
do
	dir=`dirname $i | sed -e s%./%%`
	outfile=$dir/`basename $i .png`~ipad.png
	sips -z 152 148 $i --out $outfile
done
	 
 
Apologies if I'm repeating stuff that everyone already knows, but I can't find this stuff anywhere.