13" Macbook Air (mid 2011) Freezing

I've had my new 13" Macbook Air for a couple of weeks now. It's the iCore5 version with a 256 GB SSD and 4GB of ram.

I was editing a Keynote presentation today when everything locked up. The spinning beach ball showed up and nothing worked except I could move the cursor around. Shortcut keys for changing applications or force quitting applications didn't work. The only option was to hold the power key to shut it down.

Upon rebooting things looked normal for about 10 seconds until it would freezes again. This repeated many times. I was once able to bring up the activity monitor, but nothing there looked abnormal when it froze. I tried to open the error console, but was never able to before it would freeze. I tried resetting the SMC and NVRAM with no success.

Next, I tried restoring the system to a recent backup. Everything appeared to be back to normal for about half an hour. I was back to editing the same Keynote (latest version) document for about 15 minutes before it happened again. Other programs running at the time were Firefox (6.0) and Mail. I also have dropbox running in the background.

Thoughts on what the issue might be? Hardware or software?

Thanks,
Geoff