Thousands of years is a
major underestimate. Current research suggests that the sun will be able to support life on earth for around another one billion years. Though it wont really die out for at least another five billion (Developing into a red giant, then white dwarf).
Also, I think you may have confused the clock quote with one about the length of time humanity has been around. The universe is certainly not half-way through its life - even if the universe were to 'end' in the quickest way possible (big crunch), it would take at least another 100 billion years for the expansion to slow down and reverse (Sorry, I can't find the citation for this).
Apparently the current most likely end to the universe is the Big Rip, though this would take trillions, rather than billions of years.
Edited by Magnesium, 10 August 2006 - 11:04 AM.