I left a CPU miner running on my email & webserver VPS (back when Bitcoin was fairly new and worth nothing).  I managed to solo-mine 50 BTC, but forgot about it for a while.

Back in 2013, when BTC was around $13 and I was a n00b in this forum, I used most of that 50 BTC to buy a used Radeon HD 6870 (to do some GPU mining) and a couple of Butterfly Labs coffee-warmer ASIC miners.  I still have these, though they're all idle as none of them are economical to mine with nowadays.  (The GPU, at least, was still powering my work desktop until it got upgraded a few months ago.)

If I'd held onto those 50 BTC, they'd now be worth the better part of $2 million.

Mining proceeds mostly went into a few silver purchases at first, then into buying more ASIC miners (fastest I ever bought were a couple of Antminer S1s).  None of them are economical to mine with now, so they're as much paperweights as the BFL miners.

In 2017, I decided to have another go at GPU mining and built a rig with four GeForce GTX 1070s.  In about a year, it mined enough to pay for itself.  In the recent runup in value, two things have happened: (1) it's once again profitable to run the rig (fired it up again last night, and it's supposed to clear $300 or so per month even with power at 12¢/kWh) and (2) the proceeds from the last round of mining have appreciated enough that they'll go a long way toward paying off my mortgage.  I've also bought and held some BTC, so I'll probably only put 50-60% of current holdings toward the mortgage and let the rest of it continue to appreciate.