[quote=Ashley]Due to the way graphics processors work, images are usually actually held in memory in a power-of-two size (e.g. 128x128, 256x256, 512x512, etc).[/quote]
Also in the "Remember not to waste your memory" blog, only square sizes are mentioned.
I hope you're right as it would suit me better in the long run (I won't discuss how long I may have wasted re-drawing my images to use square tiles after being advised to do so...)