I've had this problem with all versions of the 1.8 pre-release. Items in new chunks don't render properly, it's almost like I'm half in spectator mode. Occasionally I would see this in earlier versions, but it would go away after a second or two. In 1.8, it can last for as long as I'm willing to wait. 5+ minutes.

If you look at the screenshot, you can see mobs floating in the aether. If I drop down to within about 5 blocks of the terrain, then it will render properly, but only for the chuck I'm standing on. This is a very poor fix. It can make running very dangerous, as I don't know what I'm about to run into.

I've tried using fast graphics, and dropping other video settings down, but it makes no difference.

Finally, it doesn't appear to be happening on our laptop. (Also a Mac, NVIDIA geforce 9400M)