For those looking for a good bike in this range, I would consider something like a 2009 Trek 4500 or a 2010 Kona Blast. The 2010 Trek 4500 have gone to a suntour shock which is a definite downgrade. I have seen people knock the Dart shocks, and it is true that there are better shocks out there, but you aren't likely to find them in this price range. I would also suggest that you not put a ton of emphasis on disc brakes at this price level. I have found that while they don't hurt you, many of the mechanical disc brakes found at this price level actually don't give you significant performance advantage over a more traditional rim brake set up. This is contrary to popular opinions so take it for what it is worth.
If you are looking to get into Mountain Biking, this $700 point is great because you definitely can find solid bikes. If you think you may grow into the sport, I would recommend a big brand like Trek/Specialized/Cannondale as they have better name recognition and will have better resale value if you decide to upgrade in a couple of years. Most importantly, find a bike you like to be on!