I buy a lot of my stuff from liquidation outlets and pawn shops. Got an almost brand new Acer Laptop with Windows 7 for 80 bucks. I wouldn't buy a cell phone though because of diseases and shit since its on someone's ear plus its generally dropped a lot for most people. Plus most items can be repaired and upgraded.
Right now, my main desktop computer I use for my business is a P4 Dell Dimension I got for 50 bucks from a company that went bankrupt ( happens all the time) about 4 years ago....still runs like a champ. The key is to not put the latest software up all the time if you don't need it.
Even old computers can be salvaged. Got an 8 year old IBM Netvista. Instead of throwing it out, I just loaded it with a scaled down version of Ubuntu Linux and keep it in my exercise room so I can watch Hulu, Netflix, or listen to Pandora while I train.
If you don't need to spend the money....then why should you?
Because of the nature of my research and the kind of software I develop professionally, I mostly work on high-end cutting edge hardware. Most of my personal projects usually target relatively new hardware and software. Having to support 350MHz machines running Windows 2000 just doesn't appeal or make sense to me.
That's not to say that older machines are worthless. Depending on your usage model older hardware can work well. But I wouldn't run anything as old as an 8-year old NetVista myself. Even if the horsepower was enough, the extra amount of power that thing would suck down would almost cost enough to justify getting a newer, more efficient machine. Heck, I could get more performance than that out of an Atom machine that sips less power in a year than the NetVista does in a week.
It's in that sense that buying used old computers can be a false economy. It's a slightly different calculus if you already have the hardware, but still...
One thing I'd never get used or refurbished is hard drives and solid-state drives. My data is simply way too valuable.