I started building my own in 1985 with off the shelf hardware. At that time you could build for a lot less than you could buy. In many ways you still can if you do enough research and have reliable deep discount places to shop. Last year I was going to build a new pc, and I wanted a core 2 duo system with ram expansion capability up to 8 gb and a large 320 - 500 gb hd plus two dvd burners. After pricing the parts I found that I could buy a ready built system for less than it was going to cost me. (I paid $599, couldn't build for that price). Not as much self satisfaction, but it got me to where I wanted to be, cheap. This isn't always the case, but like I said if you do the research, it can happen.

The most important thing is the motherboard, and that is where all of research time should be spent. There are so many variables it's almost mind boggling. And needless to say, it is very difficult to find a motherboard at a reasonable price with all the bells and whistles that your heart desires. One good thing about building versus buying is that you won't end up with a proprietary system where many of the additional or replacement parts have to purchased from the OEM. I hate those bastards.

In any case, good systems can be had for under $500 or you can spend $3500 if that is what you desire. As for a laptop, I would never consider building one. The best rugged ones are Panasonic, but they are pricey. Toshiba's are the most reliable, but Dell is a close follower. With Dell you can pick and choose your components, which is a good thing.

The most reliable systems, desktop or laptops, are Apples, but they are not big sellers in the business world.