Even with the addition of VRAM I am experiencing the typing in IM lag that others have written about. I am averaging 20 seconds every 5 - 10 minutes.
I can be walking, driving a boat or car and the beach ball pops up and no telling when I finally come back where i will be - the SL action keeps rolling it seems. I have come back and been nose against walls, in the bushes, you name it. There does seem to be some correlation between where i have just TP'd from and the frequency of the "hangs"
I always tend to come back after waiting for the beach ball and only last night did I physically crash twice. I also have a laptop fan under the Mac book Pro to keep things cool
One other think I am also experience graphic "flashing" with regard to water of SL when I am in mouselook and pan my view - the water flashes from the water texture to white and then quickly back again this happened several times last night as well.
I realize i am pushing my luck running at graphic performance set to high and a draw distance as 128. I have atmospheric shaders on and water reflections set to off. I can not run this in Low i spent too much money on this computer not to get excellent graphics.
One last thing I am going to try running the OpenGL Xcode work around and see if this helps my experience at all.