Do any sub 20 cubers actually line up the colored blocks on PLL's before executing the PLL?
Tip: If you learn which blocks/cubies of the pattern will be in position after execution, you can anticipate AUF during PLL recognition. An easy example is U-perm: the cubies belonging to the bar are in position. If they match up with F2L then AUF will not be required. If they have the opposite colour to F2L, then U2 will be required etc..
What is hexadecimal and how would you use it to memo CO during bld?
It's a numeral system of base 16. I wouldn't use it for CO since those have 3 different orientations, but I would use it for EO since there's only 2. 0 would equal correct orientation and 1 wrong orientation. A 3x3 has 12 edges so you would memorize 100111110001 for example for edges, which equals 9F1 in hexadecimal, so memorizing 9F1 would be enough to orient all edges. It's great for BLD but only if you're used to it.
Then is there an easy way to memo CO durind bld and multibld?
This is quite old, but I'll answer anyway...
If you're good with working in base 3 then this is perfectly doable working in the nonary (base 9) system. It means CO is memorised as a 4-digit nonary number. This is just like working in normal decimal without using the digit 9.
Its done like this: For each corner assign a ternary digit (base 3).
oriented = 0, twisted once = 1, twisted twice = 2
This creates a number like: 12011021 (one digit per corner)
Convert into a 4-digit number by adding them in groups of 2's, multiplying the first digit by 3. So this number becomes 5137 (3+2, 0+1, 3+0, 6+1)
Converting a digit back into two corner orientations is quite simple.
First digit: n < 3 gives 0, 3 <= n < 6 gives 1, n >= 6 gives 2
Second digit: n mod 3 gives you the orientation. (ie, take exactly 3 from the nonary digit until its between 0 and 2).
It may seem complicated at first, but I'm sure doing it over and over it probably gets easier.