I chose 6-10 because I still regularly use a computer that I built in the summer of 2000, just prior to attending university. Give it a couple months and it will be in the 10-15 category.
It's had some parts changed out in the meantime (video card, extra memory, case, extra harddrive, new CD drive) but the guts are still the same that I put together way back when, an Athlon XP 800 processor with slot mount causing the heatsink to dangle precariously over my video card.
Despite being moved ~18 times over its lifetime (I've lived in a lot of places), one of the CPU/heatsink supports breaking, and once completely coming loose and smacking around the interior of my case while dangling by its heatsink fan connection... it still works!
It now does its part as a database server for my website, and its used on a daily basis.