I have budget ($600) for either full suspension or a hardtail. I am a beginner mtb with loads of road bike experience. I keep reading that once you get your first bike, sooner rather than later, you'll be upgrading. No matter how hard I try not to, I've followed this mantra many times with road bikes.

Would it better to purchase a low priced full suspension (like a bikesdirect Ghost 6900) as as first bike? Or buy a hardtail to become proficient at riding trails, then upgrade later?

I think you would get more "bang for your buck" with a hardtail.

That being said have you ever bought from bikesdirect? I'm thinking of getting one of their road bikes since their so cheap.

The hard tail.

For $600 you can get a mid to higher end hardtail. My dad just got a nice Iron Horse hardtail. Full Sram X.7. Avid Juicy 3s. Marzocchi fork for about $700. FSA cranks. Very nice bike with good components. If you went to route of a full suspension you are looking to spend over $1000 for a bike with comparable components. Basically in your price bracket you can get a nice, well equipped hardtail for the same price as a low end full suspension.