Hey you know what, it worked for me. I've been using my Macbook 5,2 for a couple of weeks now with 8GB ram and it works tremendously better than it had before.
Here's the proof:
It's 8GB corsair that you get in Amazon for 129 bucks.
I'm actually planning to upgrade to Lion now, and that's how I bumped into your post on Google.
Good Luck upgrading
Do you have boot ROM: MB51.0088.B06 or MB52.0088.B05? If your not sure then click on More Info and it will bring up the details.
Speaking to someone else it seems even losing the ability gained from having two processors the same and having 6GB would be of benefit but I would prefer 8GB.