I've had my i5 replacement MBP for over two months now, and it definitely does not have any problems with the screen blinking. It does not have the 9400M chip - the new models have an Intel graphics chip on the processor for battery saving mode, and an NVidia 330M for performance; the switching between them is seamless too, no need to log out...
To those still experiencing the blinking with the old model, I suggest you keep on at Apple for a fix, even if you are out of warranty. I have followed this thread before and after my ordeal of four repair jobs (and since getting the eventual replacement machine): it's on 37,634 views right now, I think it was on about 14,000 in March, so clearly there are many people with defective machines. It's very frustrating to read of more people being told by Apple that it's an unknown issue, at the very least they have extensive information from the repair jobs they carried out on my machine, and the descriptions of the problem I gave them; plus there are dozens of people reporting repair jobs for the issue in this thread. It is either catastrophically bad information management by Apple, or maybe something more sinister...?
I really got traction in getting my machine replaced after emailing some people mentioned on this page:
http://web.archive.org/web/20080725070602/www.apple.com/pr/contacts/
... it's a copy of a page that no longer exists on Apple's website. My advice is to pick some email addresses appropriate to where you live and write them a short letter of complaint (200-300 words at most): summarise the problem you have with your machine, explain how it is a significant defect in what is supposed to be a high end computer. Something you definitely would not expect from an Apple product...
One of my emails was forwarded to the right person, who really spent a lot of time and effort to sort things out for me.
Apple have given free out-of-warranty support once before with the previous generation of MacBook Pro with the 8600M (
http://support.apple.com/kb/ts2377) - if enough people write personally and complain they may well do something similar about this fault in the 9400M.