I'm not a billionaire, but I love my life and death/ageing is one of the few real problems I have.
I'd rather have billionaires thinking like me and investing their money in solving real problems than buying yachts and marrying/divorcing every year.
I know I'll get my ... kicked for this comment, but anyway.
The iPhone experience is not sterile at all. It comes with a browser and there is no restriction for the websites you can open. Google ('the web is the computer') should be the ones to best understand this.
Since when is controlling the quality and security of the content at a marketplace that you operate equal to limiting people's freedoms?
If I own a grocery shop and refuse to sell someone's rotten tomatoes does it make me necessary evil?
Not letting people charge 0.99$ for balloons in swimwear using your own infrastructure has nothing to do with their freedom of speech. They can always create a web page and show it to the world.
Learn both. Seriously. Pick a good book about algorithms or data structures, open Visual Studio and Eclipse, load the Java and .NET docs in your browser, maybe pick some introductory books on both and start coding the examples. It might take a little longer to start, but it will pay out tremendously in the end.
I've been doing this with Scheme and Erlang using SICP (http://mitpress.mit.edu/sicp/) and it has definitely helped me understand better both the languages and the material.
In your case you have two very similar platforms, object-oriented, garbage collected, with a very similar syntax. The big strengths for both are their libraries and their VMs, learning them in parallel makes lots of sense.
It is not misleading as this is explained in the comments section bellow the chart. Anyway it was just a suggestion for a possible direction to look at.
As the other guys said it all depends from your situation and what you are trying to do.
One thing to maybe look at is Erlang and related technologies Mnesia, Yaws etc.
This is a comparison of Apache vs. Yaws under heavy load:
http://www.sics.se/~joe/apachevsyaws.html
What an useless rant! It would have been better if you told us about all the great things you did about the water, the hunger, the pollution, the world peace etc.
I usually ignore critique from people who are not a personal example of what they are preaching. So would you please tell us how you put your money/brain/lifestyle where your mouth is or else just SHUT UP!
Oh and by the way entrepreneurs are people who try to create a profitable business. It might save the world or it might produce toilet paper, but if it's not making money, they can't be called entrepreneurs. So if you want them to solve any problem you consider important, don't ask them to give away money, tell them how to make more money by solving it.
The problem with the nested sets is that changing the tree can be slow. You need to update all the nodes with right/left pairs after the insertion/deletion point.
There are two more methods which can be of interest and don't suffer from this problem:
"Materialized path model" (which uses strings to encode the whole path to a node) and the "nested intervals tree encoding" (which could be the ideal solution if someone manages to implement it. I couldn't find a decent implementation):
http://arxiv.org/ftp/cs/papers/0402/0402051.pdf
It's interesting that you mention "black swans", as one of the reoccurring themes in the book is about "experts" being too close-minded and focused in their own field.
To me "hacker" is more a synonym of "curious" than of "coder", so if someone implies a rule of only submitting "coder news" they should maybe think of changing the name of the site too.