I run Minecraft, join a server running on my computer on the latest release (1.8 Prerelease1 [it has been occurring for several earlier releases as well]) and when I look at any flat area of blocks, I can see the lines in between them. I have messed with all the video settings as well, so I don't think it's dependent on any specific setting there.

I know this has been an issue for a while, I just wanted to show that it is still happening.