All editions of IJ have the same pagination (which makes it easier to co-ordinate group reads as we've discovered over at wallace-l).
The only difference between the first edition and later editions are that some corrections were made to the first released trade paperback. I thought I had a nice link to all the differences over at The Howling Fantods! but maybe it got lost in the server change a few years back. I'll keep hunting.
Nick
http://www.thehowlingfantods.com/dfwEDITHere's and example:
Hardcover/Advance Reading Copy
"You're how old, Hal, fourteen?"
"I'll be thirteen in June." (27.23-24)
"I'm twelve for Pete's sake."
"... potentially gifted twelve-year-old" (30.10-11)
Paperback/UK paperback
"You're how old, Hal, fourteen?"
"I'll be eleven in June." (27.23-24)
"I'm ten for Pete's sake."
"... potentially gifted ten-year-old" (30.10-11)