Hi
I find calculating the positions of the sun easier and less prone to error, the math is not that scary.
[soapbox] I agree with Robin2, anywhere on the earth and the LDR's will work without any calculating, also the LDRs will track to the brightest part of the sky, which is not the sun behind a cloud.
Also the sun as it approaches the horizon is diffracted so its apparent position does not follow an algorithm.[/soapbox]
Can you post picture of your project, also if you are using protoboard as in the fitzing diag, check that you have continuity down the two power supply rows on the outer edge, some have a break halfway down.
Also powering the servos off the 5V of the arduino is not recommended due to current needed to drive servos.
Tom..... 