I just upgraded from 1.4.5 to 13w02b. Now, there are cracks between every blocks. Not only solid blocks: the flowers are also affected, as illustrated by one of the attached screen shot. The effect is of course much more visible in motion than on a still picture. The effect is very visible when we see the light sky between dark blocks, but if you look closely at the grass on the screen shots, you will notice black and dark blue pixels (underground water I assume).

This was extremely rare with 1.4.5 and before: we could sometime see one orange pixel and infer the presence of lava somewhere far away down there. But now, this isn't an exception anymore: all the edges of every block always glitches.

This happens both to my girlfriend and I on two different machines.