I have a question about how you read the action check line on the action cards. I assume that whenever it is a Characteristic vs. Characteristic check then it counts as an opposed check, as it states on p.49 "To perform this action, a character must attempt the check shown here. This indicates if the check is a standard or opposed check.". So for example Ranged Shot reads "Ballistic Skill (Ag) vs Target Defence." Keeping in mind that the default difficulty for a melee/ranged attack option is Easy (1d) you would then compare the Agility Characteristic of the character against the Target's Defence and determine if any extra dice need to be added. So, lets say the character is firing at an enemy with a Defence of 1 and the character has a Agility of 4. The target's Defence is less than half of the acting characteristic and no challenge dice are added. This leaves us with a difficulty of Easy (1d) as that is the default. If the enemy had Defence 2 then it would only be less than the acting characteristic and add +1 challenge die to the difficulty making it an Average (2d) check.
Before when I was reading examples of combat people made it sound like a melee/ranged attack is always a Easy check and I don't believe this is the case. I also believe this would answer the question of how to figure out difficulty values for spells that has been such a big topic. For this example let us look at two Bright Wizard spells, one containing a standard check and the other a opposed check in the action check line.
The first card is Flameblast which states "Spellcraft (Int)" in the action check line. This is not an opposed check, so there is no modifiers to the challenge dice. However, the spell has an inherent challenge of Easy (1d) as listed on the top left corner of the card. So, as this is NOT a melee/ranged attack there is no default difficulty and you would just add the 1 challenge die. This is of course if you are not engaged with an enemy as the card's Requirements state that you add an additional challenge die in that case bringing it up to an Average (2d) check.
The second card is Great Fires of U'Zhul which states "Spellcraft (Int) vs. Target Defence" in the action check line. This is an opposed check so we must consult the table for opposed checks to see the challenge of casting. For this spell we will assume an Int of 4 for the character. This card, like Flameblast, has a difficulty of one challenge die listed on the top left of the card. So, if our Target had a Defence of 1 zero challenge dice would be added (1 is less than half of 4) and the total challenge would be Easy (1d). If the Target had Defence 2 than +1 challenge die would have to be added according to the table and the total challenge would be Average (2d).
So we can see that Flameblast is relatively easy to cast as no matter what the Target's characteristics are the difficulty will not raise. Great Fires on the other hand will become more difficult as the Target's Defence increases.
To give one final example look at Magic Dart, a petty spell. Magic Dart is a Spellcraft (Int) check with an difficulty of one misfortune die. As this is not an opposed check challenge dice only enter the equation when the Requirement of "If you are engaged with an enemy, add <P> to your dice pool" is met.
I am pretty sure this is how the cards were intended to be read and I hope someone can either confirm or deny if this is correct. Like I said, if this is the correct way to read the Action Check lines then I think a lot of people's questions about spellcasting difficulty would be answered.