My MacBook, an original white 1.83GHz Duo Core, was upgraded to 2GB of RAM from the stock 512MB. It ran pretty well until I upgraded to Leopard. Soon after I was having frequent kernel panics. Eventually DiskWarrior was needed to bring my MB back to life after some serious corruption.

I put the original 512MB of RAM back into the MacBook. It ran kernel panic free for several days. I had run Memtest in the past and it never found any problems.

This was enough to try new RAM. I looked up the receipt for the RAM. It was no longer under warranty. I paid $176 for it almost three years ago. Today that same 2GB cost $30.

Several days after installing new Crucial RAM (the original 2GB was some other brand purchased at NewEgg) I have not a single kernel panic. There is no way I could have gone this long without a KP on the old RAM.

It's still a wonder to me that the RAM simply went bad. Trying to remember way back I think my MacBook did have kernel panics from the start, but they were pretty infrequent.

Update

It has been more than two weeks since installing the new RAM and not a single kernel panic. I was in Italy for eight days with the MacBook where it got quite a bit of use. I have regained the confidence I lost in my MacBook.