Kurt J. Mac has been walking in the same direction in Minecraft since 2011. It is now September 2015, and he is still going.
Profiled recently by Guinness for their records book/marketing catalogue, there's a progress report from April 2015 in there, saying that as of five months ago he'd crossed 2,097,152 blocks. Equivalent to 2,097.15km. (He's obviously gone further since.)
Remember, though, he's not just walking for the sake of it: he's trying to reach Minecraft's "Far Lands", and despite the fact it's taken him four years to get as far as he has, he's still only 16.78 per cent of the way there.
To give you some kind of representation of just how far that is, check out the scale of this map of his current progress:
Kurt's walk isn't just for kicks: He's doing it for charity, and you can donate here.