Just to add to the plethora of posts that are already out there I'll give a brief description of my problem.
I'm running D3 1.0.8 on a Macbook Pro late 2008 model. My system is osx 10.8.4.
The game runs around 45-60fps on medium to low settings depending on the amount of action on screen. Usually a couple of minutes into play the framerate will suddenly start rubberbanding down to 15 and then back up to 40 or 50. This continues infinitely no matter the environment or the amount of action on screen.
My internet connection is not the issue it's streaming the game data plenty fast. At the worst my latency is at 300ms.
Here is what I've tried to fix this issue myself.
1) Checked my "energy saver" settings to make sure I wasn't running on the lower performance integrated chip.
2) Restarted my computer.
3) Zapped the PRAM
4) Deleted the D3 prefs and plist files
5) Uninstalled and reinstalled D3 completely
I can only conclude that this is an in game bug. Anybody else with this problem found a solution? Let me know!