I decided it was time to reboot my digitalocean machine after installing a new kernel. Its uptime was: 
 17:14:28 up 368 days, 19:55,  3 users,  load average: 0.29, 0.10, 0.07
Since that's a year I suppose that in that time it's cost me about $60, minus some for the referrals I've gotten for posting about them on my blog.

.. I actually had to reboot it twice because I didn't know you had to change the kernel version via the control panel(!) but no harm done.

Anyway, in that time I never noticed any blips in functionality or connectivity, though on a couple of occasions they credited me a few cents for a service interruption.

All in all, it's quite a solid service!