I don't know if this is a bug, or my computer, but I opened a world in 14w26c. I was getting my typical post 1.6 frame rates (around 20-40 fps). I wanted to see the new mobs, so I grabbed the spawn eggs for the Guardians and tried to spawn them. After multiple tries in and out of water, they wouldn't spawn. I then tried a different mob, and still nothing. About 20 seconds later, everything suddenly spawned. The amount of server lag made the game unplayable.

I don't know if others will be able to duplicate this, but I can provide footage of the lag if it happens again. I have experienced this kind of lag in previous 1.8 snapshots.