I've never used PNY in a mac, but I have used it in a pc. From my experince it was the crappiest ram ever.
1. I got 256 pc 133 for my aunt and I had to replace it 4 times because it would not be reconized. I found out that it wasn't compatible with the crucial ram in the other slot.
2. I got some later for my girlfriend when I built her pc and I had to return it twice because it kept blue screening the computer. After she had it for a few months, I didn't like the performance and I went and got her some crucial instead.
I have better luck with no-name ram. Maybe I'm just unlucky and got some duds, but I personally would never buy it again.