Some more background on this (the patch notes needed another edit that did not make the deadline, as 2.4.1 was on a very tight schedule, alas)
We ran into a bug in WoW code that was triggering the panics and visual corruption when certain spells are played. The code path in question would get into trouble on machines in these categories:
10.3.x or 10.4.x (any version) PowerPC with ATI video
10.4.8 or lower Intel with ATI video
For 2.4.1 we were in quite a hurry to get the crashes and panics to stop, so we simply disabled the drawing of those types of effects on the configs listed above. This has the side effect of making some things in the game not show up. There is a workaround you can do until we ship the real fix in 2.4.2. Don''t bother with any of this if you are on Leopard, or on NV or Intel graphics.
in config.wtf:
SET M2UseShaders "0"
SET AvoidTigerPanic "0"
The latter setting is what disables the drawing of the affected items (mostly spell effects that are projected onto terrain), the game defaults it to "1" on affected configs listed above. The first setting disables the use of shaders for those types of effects (otherwise you would run into the crash again). Warning, the game may not run as quickly in this config, but no effects should go missing.
The "AvoidTigerPanic" setting will become a thing of the past in the next patch. We just nailed down the precise cause of the original bug today, so we can fix it decisively in 2.4.2.