I'm considering an SSD for my MBP. Since they're so expensive, I'm considering a 120 GB drive. I don't store a lot of info on my MBP - I use it mostly as a "terminal" and access my data through the cloud. But I'm wondering if SSDs require a significant amount of free space like normal hard drives do to perform at their best. For example, would a 120 GB drive slow down considerably if there was 100 GB of data on it?