would have put this as comment, since it only completes the answer of Santosh, but i have no right to comment :)
since i lost some nerves over it (sorry if i am too dumb), having my app ignore the alternative layout-x folders and so as to spare others, and since its not written explicitely in the android docs/tutorial about different screen sizes (a link reminding this would have been nice...) , if in your manifest you have not this type of directive, all the above won't work.....
<supports-screens android:resizeable="true"
android:smallScreens="true"
android:normalScreens="true"
android:largeScreens="true"
android:xlargeScreens="true"
android:anyDensity="true"
/>