I have not ever had a store-bought machine because all of mine have either been custom designed in the early days to my specification and all since then have been built by me. However I have been to other people's houses who have big name desktop machines and they have always been slow with seemingly cheap components. Such as a good graphics card but it is the cheapest of the cheap version where it has no casing around it and has a weak fan.
Is this a typical thing that store bought means not as good? I personally just like to know exactly what goes into my machine so I always just build my own. I bet it is cheaper too, but I am interested in your opinions.