I purchased a Macbook Air about six months ago. I love it. However, it falls asleep whenever it damn well pleases and then doesn't always wake up when I use the space bar. Sometimes it wakes up when I jossle it a bit or close and re-open, but this doesn't always work....I actually took my original in with this issue and they switched out computers, so I got a new one, but it's doing the same thing! Anyone else having this issue?