A couple of people have asked me recently about how resiliance and defense skill combine to make one uncrittable. Here are some of the numbers: (all for level 70 toons)
60 defense rating = 25 defense skill = 1% critical hit avoidance
39.4 resiliance = 1% critical hit avoidance
It appears you need the combined critical hit avoidance to equal ~20%
If you have a defense skill of 350 you need 225 resiliance to reach uncrittable
If you have a defense skill of 370 you need 190 resiliance to reach uncrittable.
If you have a defense skill of 490 you don't need any resiliance to reach uncrittable. This is how most PvE tanks reach uncrittable.
There are many cool formula calculators available at
www.tankingtips.com - click the link in the banner at the top.