The Alternative DIY Approach, Cooking The Books:
I think it's safe to assume the firmware update released, and those possibly yet to be released, are only to mitigate issues with these GPUs, (i.e. under-clock them). Deducing purely from the fact that the update seems to ether completely eradicate or only reduce the flicker for various people.
If it works for you then great… don't try this. For those of you who it didn't work for, and are out of Apple care / warrantee etc, and have a seriously defective model (bad enough to risk this) An alternative might be to bake your logic board...
If you read back far enough in this thread and do enough googling you will find that the cause of this problem is the use of high lead solder for the GPU die (nVidia's fault)… It was also found that revised macbook pro boards used to replace the defective ones only had the good solder on the MCP79 Chipset (host to the 9400M) while the 9600M GT remained with the bad high lead solder, which kinda makes sense of all the recursive logic board replacements.
Basically if you do a lot of gaming on this thing and kick your GPU(s) into overdrive often then these "bad bumps" will get micro-fractures much faster than normal, which will probably translate into increased flickering or other screen artifacts, or even complete failure. This isn't completely uncommon on other GPUs, just usually happens when they are way older, and / or have had a lot more use, because they don't have defective solder.
For the Brave, Baking Your Boards:
What you can do is attempt to reflow the soldier and fix those micro-fractures by heating up the whole board briefly to the melting point of the soldier. This is most commonly done in a conventional oven, but you will need to remove the logic board, and then strip it of anything that can melt, you will also need to remove heat syncs, and thermal paste, so this definitely isn't for the faint hearted.
I shouldn't need to tell you how much of a risk doing this could be, but thought some of you with seriously defective models and some ifixit goodness could give it a shot if you don't mind risking having a useless and toasty macbook afterwards. Google is your friend here. But here are some links to get you started:
http://russell.heistuman.com/2010/04/27/cooking-the-books-or-baking-my-macbook-p ro-logic-board/
All of the books i can see here are older than the models in this thread, so the deconstruction will obviously differ for your model (check www.ifixit.com) the unibody ones are way WAY easier to take apart, however the preparation of the board and the process itself will be the same.
http://russell.heistuman.com/2011/05/09/baking-a-macbook-pro-logic-board-video/
This is a neat video of someone doing it start to finish (still older model) see how he even removes the thermal paste etc, (you will of course need to get new paste and read up on how best to apply it) otherwise you will only fry it when you put it back together... more on frying next week, lets stick to baking.
One thing to note though is that even if this does work for this model... it will only be temporary, as this wont change the composition of the solder, just reflow it, it will eventually crack again if subjected to enough stress (heating / cooling). Then again it could give you an extension of life equivalent to the date you got the model to the date the first signs of the issue started. (as if it were new)
Good luck, if you try this.
I don't claim any responsibility for your toasty boards.