Here is a new reply to the question of whether your chair is still a chair when you don't observe it.
The answer is - it depends.
We live in a giant cosmic hologram, and whether the chair exists or not depends on the holographic projection of physical processes that take place on a distant, 2D surface.
So say the scientists.
Our world may be a giant hologram - space - 15 January 2009 - New Scientist