Hi,
Ngui and other 2d frameworks comes with widgets called "anchor" and let you stick a gameobject in various screen positions ( top left, bottom right, center, etc), and they adjust with any screensize, that's a very very powerful way to describe your ui so that you limit problems with screen sizes variations.
Also, GUI Texture comes with a relative screen transform position, that may help you as well ( play with a guitexture x and y position to see how it relates to the screensize).
Unity GUI also has some tools to do that, for example, if you create a full screen vertical guilayout, and in there have a flexible space then a button, that button will stick to the bottom.
Bye,
Jean
bye,
Jean