Using a seemless texture is one of the most popular, and easiest way to create a nice scalable background for use on anything, all it requires is the use of the offset filter and a few different tools, like smudge and/or clone.
Making rounded corners in photoshop is pretty darn easy with the use of alphas. You can make a crappy lookin square into a pretty lookin rounded... square... Use it to round corners on anything really!