That loft isn't going anywhere. The 4x4's in the corners are more than sufficient to carry the weight of probably a half dozen people in each of the beds simultaneously. The 1/2" stainless steel bolts, which I see were used gratuitously throughout construction, will be the last to fail -- more likely they'll shear and/or tear the wood in half. The cross spans are similarly bolted to the 4x4's and the span isn't such a great distance that a center support would be needed (especially since it's a 2x8, 2x10, or 2x12--i can't tell from the picture).
In my dorm days, I had almost the exact setup, except our beds (the same frames it appears from the picture) were hung from industrial strength stainless steel chains and suspended from eye-hooks anchored through the cross spans. It was quite an experience getting into a "hammocked" bed at night WITHOUT a ladder which we never got around to building. Ours was built in a day, stood for 2 years, and torn down in hours. Sadly, I don't think my roomate or I got any pictures of it except in the background of other photos.
techfuzz