great article. But there is a much easier way to achieve the same result. You can use UIBezierPath.
So for the above example you can just do the following:

- (void) drawRect:(CGRect)rect
{
CGRect frame = self.bounds;

UIBezierPath* path = [UIBezierPath bezierPathWithRoundedRect:frame cornerRadius:5.0];

[[UIColor blueColor] setFill];
[path fill];
}

It’s less code, you do not have to care about releasing the path because this is all handled by the UIBezierPath and you can reuse it as it automatically saves the graphics context for you. For more details see the UIBezierPath reference.