The point that cannot go unnoticed after reading some very persuasive points for all sides of this particular issue is that on November 5th 2008 the most powerful man in the free world will not be Barack Obama, it will not be John McCain or even Bob Barr, but rather Anthony Kennedy, and therein lies the problem.
Remember that 7 of the 9 current Justices were appointed by Republicans. You would think if there were party line votes, things would swing much more conservatively.
McCain is the most liberal Republican to run for President in my lifetime, and probably ever. There is very little chance that his appointees would be any better than Bush Sr.