Main take-aways are:
-Elemental resistances function as expected in addition to plain spell resistance.
-Sharpened trait is completely broken and unfortunately is probably part of the cause for the huge outcry of magical abilities being overpowered compared to stamina/physical attacks.
-The urban legend of "spell penetration is additive against resistances" is completely false. They operate as a percentage of your enemy target's resists in a linear fashion as expected.
Below is my testing table, and apologies for anyone at work who can't load the large image but it is far too much testing to post in text form.
CLICK FOR LARGE PICTURE FULL-SIZE:
http://i.imgur.com/XSs1Lue.jpg
Additional testing was completed but not included as it was done to spot-check conclusions made.
Update... 2:25am 9/12/2014
Cyrodiil decided to spin-up for me as I was about to log over to live, so I did a couple of the further tests that could be done readily. This table was done to check unmitigated damage values and to prove/disprove shielding abilities not factoring in mitigation was working correctly. Additionally I tested the Aether 5pc bonus (10% debuff on spell/armor resistances on enemy) to ensure they worked.
Take-aways from this data:
-Shields/absorb bubbles providing unmitigated protection works as the common working knowledge is told, aka properly.
-Aether light armor 5pc debuff works as intended and actually even applies a 10% resistance debuff to the target when checked on the character sheet of the debuffed enemy (listed values are lowered).
Below is the extended part of the testing table (ignore the bottom, it is for upcoming flame lash testing and other results

+ sorting out criteria):
CLICK FOR LARGE PICTURE FULL-SIZE:
http://i.imgur.com/RArdw2s.jpg
Testing remaining on current short-list:
-Sharpened on 1h (against magical resists)
-Sharpened against phys/armor (1h, bow)
-Sharpened trait only with no passives (isolate sharpened 100% exclusively) (reddit request)
-Flame lash or nb skills against flame or spell resist/armor and seeing dmg scaling (potentially checks both?)
-First-Wave Closed Beta Tester of the Psijic Order, aka the 0.016 percent.
Exploits suck. Don't blame just the game, blame the players abusing them!
-Playing since July 2013, back when we had a killspam channel in Cyrodiil and the lands of Tamriel were roamed by dinosaurs.
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-In-game mains abound with "Nerf" in their name. As I am asked occasionally, I do not play on anything but the PC NA Megaserver at this time.