*** How to solve massive LAG-related playability problems on a MacBook Air mid-'11 (possibly others!) definitively! ***
1st Follow the step by step guide to modify EXCLUSIVELY the ***trilinear filtering***, deactivating it using TextEdit - piece of cake, really, nevertheless a great tip - (link: http://osxdaily.com/2012/06/01/improve-diablo-3-performance-in-mac-os-x/) --> BIG thanks to OSX Daily. Without this tip nothing else would do the trick <-- .
2nd Deactivate shadows (another great tip, this time from the D3 forums, that deserve a big thanks! This tip made possible for me to play D3 with low res, but all the way up to lvl 60 with friends!). But as now there is a step 3, just go ahead and set texture [HIGH], Anti-Aliasing [ON] (and finally get rid of the Low Effects, turn this option OFF from now on ';D ), all on the full screen with normal mac recommended resolution for the mid-'11 MacBook Air (of 1440x900).
3rd, the trick: (trust that one!) Change Max FPS on foreground and also background to 16. No, I am not crazy. Test it.
After testing dozens of configs/edits of FPS/trilinear/shadows/effects of all kinds since Diablo 3 first launched, all this together did the trick. I think the reason is related to some failure of the Intel HD Graphics 3000 (and possibly others) to be a little more resilient when it comes down to raising FPS back to a playable rate after being hit by a heavy load while on a high FPS.
Now exit Diablo 3, restart your Mac and ENJOY!
No more monsters appearing by your side with no good reason (some are teleporters, ok, but not every single monster of the game!). You now can SEE THEM COMING AT YOU with all the images on high quality, including those background war scenes which happen far away! All without stressing your graphic card (or you) anymore '=DDD
Note to Blizzard: the graphic card was stressed so badly on the normal setup that the macbook air had to be restarted after playing D3 on my machine, until I started to use this setup shown above (also many just before playing, but this was Firefox 12-related resource-hogging behaviour after FF12 was closed - this damn app let some garbage coding behind that directly caused D3 to not being playable after surfing the web with it).