I've got a 2007 model black macbook and have recently noticed that it's struggling quite a bit to run my day to day programs. HD video playback from the hard drive will sometimes be choppy, even when I run VLC alone, and YouTube videos stutter every 10 seconds or so (I originally thought this was an issue with chrome and flash, but haven't been able to fix it through any of those routes). These problems are always more noticeable when there are other programs running but are always present none-the-less. At first I thought I was lacking RAM, but I've upgraded from 2 to 4GB without any noticeable difference. Lately it's gotten even worse, with iTunes starting to stutter occasionally, especially when Time Machine is backing up. Is my macbook just in need of a replacement, or is there something simple I'm missing?