I have the same exact machine as you the mid-2010 MacBook Pro 17-inch with 4G RAM.
This clunky at best smart-switching between the NVIDIA/discrete and the Integrated/Intel chipset has always been problematic in my opinion. It reminds me of what it would be like if a vehicle with a gas and a diesel engine and switching between the two engines actually existed. How smooth could it really be in real time?
Well, this kind of scenario does exist on the MacBook Pros you and I own.
I've found that it is visually glitchy during the aftermath of a switch--videos often freezing, artifacting then continuing for example. I eventually installed the CUDA drivers directly and now have a Preference Pane CUDA panel that has up to now provided me with information on when I needed an update. There is an update needed apparently right now but as of yet--unavailable. If it follows a typical progression, one will be available in a couple of weeks or so. This may time with a 10.7.1 update/fix for the issues plaguing the folks here.
Either way, I reiterate for you especially, but for anyone who still has a MacBook Pro under warranty: RUN THE HARDWARE UTILITY on the Snow Leopard install DVD. I'm close. My ''due date'' is September, so I will be doing this TODAY when I don't need to be working because the ''thorough'' hardware check will take a while to run.