jemagee,
I've always - ALWAYS - built my own machines. As a result, I tend to run a bit longer than most people on the systems I build, since I generally build to a pretty high spec. I'm 5+ years on my current (desktop) system, and still going strong. My issue is generally storage space, since I do some video editing.
Generally speaking, unless you want *THE* machine, there aren't a lot of benefits cost-wise of building your own. There are, however, a lot of benefits CONFIGURATION-wise. By building your own system, you get *THE* parts that you want, and if you're looking for a trouble-free system, that's the way to do it.
The other nice thing about building your own machine from the ground up really hits when you get to the OS. You install what you want, and *ONLY* what you want. Most pre-built systems come with tons of junk that you really DON'T want, and can't get rid of all that easily. The other big downside is that they go cheap with OEM licenses - which I hate. If I wanted to do away with my current machine, and get a new machine, I could re-use my XP license...but, then again, I paid more for it. And I went with the XP Pro, rather than XP Home, meaning I can make use of my nice network and can set my machine up to connect into my domain.
The downside is that if you have trouble, guess who tech support is. If you're experienced, or have a friend who is actually really good with troubleshooting (which is a lot more rare than most would have you believe), you're in good shape to do your own machine.
Another downside is that hardware changes FAST, and you have to keep up with it to know exactly what you're dealing with, and that the parts and pieces that may go bad in your system are still replaceable a couple of years down the road. If you don't keep up, you may end up looking for a piece that is currently obsolete to fix your machine that's a few years old.
I tend to be pretty picky with my systems. I want a keyboard that feel just so...not just any keyboard will do. I like my Kensington Expert Mouse trackball. I want specific things out of my Sound Card, graphics card, network card, etc. It may be something as seemingly trivial as having a configuration layout like I expect, or it may be as picky as being able to find the toner for my printer at any store 7 or 8 years down the line. I want it to fit in X amount of space, have X amount of expansion, etc. And I want it from specific companies; no more of going with a reasonably no-name company and then finding out 2 years down the road that they're not releasing drivers for the new OS that's coming out.
The more picky you are, the more likely you're going to want to build your own machine, partly - and only partly - because you know the difference between what you WANT and what you're liable to get "off the shelf."
That said, there are "lemon" products from big names out there. Every once in a while, there's a product that just doesn't live up to the company's reputation - and that's another downside to going "bleeding edge." Then again, sometimes, you get ABSOLUTELY KILLER products - like Skander can tell you about when he got his video card, or me getting a keyboard in 1991 that I still use today.
A big part of the reason I'm so picky is because my home network is rather involved; rebuilding the whole thing would be a nightmare, and so I have to pick and choose which things DO fit the entire scheme and which things DO NOT. By putting a little forethought into things, I generally have a replacement part in one of my other machines in the event something in a more critical machine goes down - and part failures generally don't happen too often for me. <knock knock> And having the whole system gives me a bit of a piecemeal way of incorporating new technology.
There are lots of pluses and minuses both ways. I just generally hate the minuses from pre-built systems to such a level that I'm willing to fork over the extra cash to "do it right" up front, and keep my system in place for an extended time.
