[sorenjan]

I'm pretty sure my Pi failures where due to weak power supplies. I tried running a Raspberry Pi 1 B on a 1 A power supply, and after a few months it wouldn't boot. Since then I've switched to a bigger SD card (16 GB) for better wear leveling, and a 2,5 A power supply and haven't had any issues yet.

[sgt]

It's often a combination of the power supply and the type of SD cards, but eventually you will have a failure no matter what SD card you use. I've learned this the hard way from running dozens of Pi's 24/7. Looking back, I regret the decision to use Raspberry Pi. See my comment below.