Putting a bit of thought to this, these are my opinions on the subject presented here (I know, I know, it's pretty much dead, please thread nazis, don'r report me ):
Was Japan ready to surrender?
Yes.... buuuuttttt, the surrender they where offering was almost certainly never going to be accepted by the allies (the Potsdam conference had established only unconditional is surrender is acceptible).
Would Japan eventually (without the bombs) offered unconditional surrender?
I say yes, and the reason why is that they did that after the dropping of the a-bombs. They where, in general, very much against it but given the destruction and death of the bombs, they where convinced. It seems reasonable to say, enough fire bombing death and destruction, they would do the same. I suspect a lot of this is honor bound. To fight and die for the Emperor is certainly very honorable (maybe the most honorable), but to die from bombs dropped from the sky, not so much.
Did the US need to drop the bombs?
No.... buuuuuttttt, dropping the bombs was likely the most "humane" thing to do. Fire bombing until surrender, or invasion would have caused FAR more US AND Japanese casualties. Yes, the bomb saved Japanese lives (radiation poisoning sucks, but so does sever burns or burning to death).
Did the US need to invade (if there where no bombs)?
I say no, and I find it a bit absurd that it was the plan (spring of 46 I believe). In a way, I suspect, the Japanese wanted the US to invade. Why? As noted above, to fight and die for the Emperor and the homeland, is the height of honor. I feel confident LeMay's (a bit of a ruthless bastard) assertion that isolation and firebombing would eventually bring them to full surrender. Firebombing would have been FAR less expensive in lives or resources then invasion (and FAR FAR FAR less expensive then the a-bombs considering the whole program)
Why was the US insistent (planning) on invasion?
Because frankly, that is what generals and admirals do, and that is what they had been doing, rather successfully for that last few years. What of the casualties? well, that is the cost of war isn't it and not as large a concern to generals and admirals (especially back then) as it probably should be ("...and the generals sat, as the lines on the map, moved from side to side..."). Of note also, especially during that era (the creation of a strategic air force), there was a very big rivalry between the Air Force and the other branches (sick, but true).
How to the Russians and the inertia of the Manhattan project factor in?
I suspect they where an influence, but not really that much. The Russians were really not much of a concern considering we had to help them invade (their invasion of the Kurals was part of the Potsdam agreement). For the Manhattan project, I am sure there was a very strong inertia to bring the program to it's planned conclusion, but as noted, that likely only saved lives. I suspect it made the decision a bit easier though.
Do I think we should have dropped the bombs?
Certainly. As noted, it very likely saved a LOT more US (because the insistence on invading) and Japanese lives then it cost.
Does current political idealism affect peoples view of history?
Very sadly, I say yes and I think it really really sucks. This goes for the "the Japanese would never had surrendered, if you say the bombs weren't necessary you are and idiot" and the "We didn't need to drop the bomb" crowd. Intentionally teaching people "wrong" for whatever reason, has always disgusted me.
In conclusion:
Despite my disgust of the last point, I do thank everyone for discussing this topic. It has made me review what I know and look into the topic. I had originally thought there was a bit more motivation on Japans part to surrender (I was not considering the assertion of unconditional surrender properly) before the bombs and never really thought of the bombs saving Japanese lives.
I hope others have learned something also and long threads are NOT bad.