On lower-end hardware (a laptop with an integrated AMD GPU running Linux), the performance hit is much more relevant. Enabling clouds drops the frame rate to an average of 30 from 45-50.
Set my Minecraft to use 180MB of RAM, (which is the lowest I could get it to go, 100MB didn't work), then loaded a world. It shows the same screen, just with a different way to reproduce.
Nobody? I'm sure this isn't a duplicate...
The issue is not reproducible in Minecraft 1.7.10 or earlier, so it's likely to be a performance degradation from recent updates given that clouds have not changed visually at all.