http://www.backcountrygear.com/bugout-elite.html
I assume the main downside is the weight penalty. A bug bivy and tarp combo would probably be lighter, as would a hammock with built in mesh. If the netting is not removable, you just end up with a heavy tarp for those times you don't need the bug protection.
That aside though, I could see this being useful for use over a lightweight hammock, or groundsheet or bivy. I reckon one about 8ft square, at about 1kg, would be a pretty competitive entry for lightweight summer camping.
Is the reason no-one has come up with this before because it's not that useful?