I don't really have time to reply in full, but here's a poem by Ronald Knox, inspired by Berkeley's "esse est percipi". Anyhow, here's the poem:
There was a young man who said: 'God,
Must find it exceedingly odd
To think that the tree
Should continue to be
When there's no one about in the quad.
To which there was an anonymous (as it so often is) reply:
Dear Sir: Your astonishment's odd;
I am always about in the quad.
And that's why the tree
Will continue to be
Since observed by, Yours faithfully,
God
Anon... I have great respect for that guy. Most of the things I find fascinating come from him. ;-)