We have gained things that aren’t negative…. But not necessarily the ones we had sought in the first place.
One big thing we have now is a true military understanding of what future wars are going to be like. The military has always had the problem of “fighting the last war.” That was true with this one. We sent in 100,000 troops, tanks, jets, cruise missiles, battleships, aircraft carriers, etc….. When our enemy was hiding in the shadows, making raids and leaving bombs. We wasted entire cruise missiles on empty camp sites that could be rebuilt in a day. Today we know how stupid a lot of stuff we had (and were building) was. We’ve modernized our military to the threats it will likely face in the future, and it wouldn’t have happened (at least not to the scale it did) without those wars.
We did put a democratic government in Iraq. As much as its a rather unstable one, it is currently maintaining itself (our troops there are just for “back-up” and are involved in few missions these days). Now whether or not that nation will survive in the long haul, remains to be seen, but the events of the past few years there do give hope. Its an entire question all together as to whether or not we should have gone there in the first place. Saddam was clearly a bad man and the world is far better without him, but we went after him on clearly false pretenses (WMD’s, aiding al-queda, etc).
We did remove the Taliban from power in Afghanistan, and install A government. This is less of an accomplishment because the Taliban are still a strong force in that part of the world, and the government we installed is riddled with corruption and shortcomings. If we left today, it would likely collapse into civil war. BUT, for the moment at least the Taliban are gone.
Without the wars we likely wouldn’t have obtained the intelligence that led to OBL, or KSM, or countless other terrorist masterminds. Not to say we may not have got them in other ways, but the people picked up in the wars made that far easier to do (despite Bush and co having screwed it up for so long).
Now obviously there is a list of negative things (which many people before me have expanded on)... but there were some good things to come out of it.