same thing here.
found out that many mbp mid 2010 are affected. there is two explanations. logicboard needs to be replaced. software-bug. i dont know yet. hope apple will take care about that. just know that many users have the same problem. it happens when the grafic switches from integrated intel to discrete nvidia.
apple had similar problems with the older mbp from 2009 and 2008. there is a repair-extention-programm.
hope if logicboard is the reason the will do the same with mbp mid 2010
Just to add to this topic. I also have a 2007 MacBook Pro with a NVIDIA 8600M GT card which, since the installation of Lion, has suffered from screen flashes, beachballs and frozen screens. Often I have had to re-power and re-set using the power button three times in a row before getting the computer back into a usable state. Having read more than I want to about these issues, I have done a complete disk re-format and re-install of Snow Leopard (rather than Lion) and I still have the problem. This morning I ran the PC TechTool that came with my MacBook and this installed correctly and it has given me a 100% pass on all the hardware. I am fast running out of ideas and hair. My MacBook Pro is pretty useless until this issue is fixed. Grateful for any thoughts and ideas. Apple please take note.