In '95, I bought a Packard Hell Pentium 75 mhz with some tiny amount of ram and a Powerbook 5300 with 8MB ram. The Packard I over clocked to 90 mhz, and maxed out the ram. As I recall, I also ran into problems upgrading some of the components because of the daughter card used for cards.
The Powerbook was upgraded to 16 MB ram for over $300. It still ran a few years ago, but has system 7.5.5, so there's not much it can do currently if it still starts.
The Packard was given to my wife in 2000, and the Powerbook I just stopped using in 2000.
In 2000, I bought a Toshiba Pentium 4 laptop with 256mb ram upgraded to 512mb. I stopped using it as my main computer in 2005. It still runs but only gets used for Diablo II LAN parties.
I have a 2007 Mac Mini bought re-furbed running Leopard maxed out at 3.3 GB RAM. It's got a strange shutdown problem and I stopped using it about a year and a half ago in 2012.
My wife is running a 2010 13" stock Macbook pro with 4 GB RAM and the 250 GB hard drive.
My current computer is a 2011 13" Macbook pro upgraded to 16 GB ram running 10.9.4.
In April 2013, I got my sons matching HP laptops with 4 GB RAM running Windows 8.0. The two problems I have are that they keep ruining their power cables, and I finally got tired of viruses, adware and malware, so I've put them on locked accounts, and they have to have me or my wife okay new software.
Finally, I have a store-bought PC with 16 GB RAM and Windows 8.0 which is basically a file and print server, and is the only desktop in use in the house.
I've got about 3 PCs I built myself and a laptop in there for family use, which were usually run for 5 or 6 years each. I tend to upgrade for performance improvements, and then hand working machines to family and friends if I know I'm giving them an upgrade too. With many of the PCs, I've had to replace motherboards, cases and power supplies, sometimes more than once. Even avoiding the cheapest components is no guarantee of longevity.