If you have the time and patience, I highly recommend doing it yourself. It can be very rewarding. You'll get to learn about the actual parts in your computer. What they do and why quality matters. This can help you later on if a problem develops and you can easily remedy the problem w/o either tech support or a costly trip to the PC repair shop.
But its not for everyone. This is why I don't push people into doing it right off the back if they are very green in the PC department.