Sometimes, but it's kind of a case by case basis. I had a 17" first gen MBP, and after I tried putting in more than like 2GB of RAM, it wouldn't even POST. However, I have seen other models where people have put like say 8GB into the Aluminum MacBook and it worked fine.
If it were me, I wouldn't risk the money. If you have the RAM sitting around, or someone is willing to give it to you, then you have nothing to lose. But what happens if you buy more RAM, put it in, and it doesn't work? So, do not spend more than you are willing to eat if things go a bit sideways.