That's alright mate, But you need to watch where you blur, blur the background, not the cars. But if you do blur the cars blur all of the car, not just the roof
edit: I got a little something in the works for you hazaky - Ok, finished it
You should duplicate the base layer, Add the blur to the duplicated layer, then erase parts you don't want blurred. Other than the messy blur, that pic looks alright.
Don't use gaussian blur for that! xD, gaussian is for smokey effects, use the regular blur to unfocus the background, so the viewer focuses on the main subject (the car)