In stock form, here are the problem.
No column brace. Watch this video I made to demonstrate. You can see the column flexing backwards from the force as it attempts to drill 1/4" holes through steel.
http://www.youtube.com/watch?v=Siwbp9Pfm4s]CNC X2 Column Flex - YouTube
The Z axis rack is not very accurate, and has a lot of backlash.
The gibs are a bad design, and need to be adjusted regularly.
And then there's just general production issues. Depending on where you buy your X2, you could get a good machine, or you could get a complete POS that needs to be completely rebuilt before it's any good.