I have another Q: there are many spells that remove or dispel enemy magical protections. What's good, and what's useless?

Here are some that I can think off of the top of my head:

Remove Magic
Dispel Magic
Ruby Ray of Reversal
Khelben's Warding Whip
Breach
Pierce Magic
Spell Strike

While we're at it, how about the spells one uses to get rid of invisibility, misleads, mirror image, sanctuary, etc, etc, etc:

True Sight
Oracle
Invisibility Purge
Detect Illusion
Probably a few more, but can't think of any more right now.

In the strategy guide it has all the counters in the game...if you want I can email it to you.

The basic mantra I follow when dealing with spell protections.

1) Cast Ruby Ray of Reversal
2) Cast Khelben's Warding Whip
3) Cast Breach

When encountering a Mage with Spell Shield or Spell Immunity:Abjuration, repeat step one twice.
When encountering a Mage with Spell Shield and Spell Immunity:Abjuration, repeat step one thrice.
When Mage has more than 4 spell protections, repeat step two twice or more.

Other useful counterspells include Pierce Shield, Lower Resistance, and Secret Word.

As for invisibility, True Sight is the end-all, be-all counterspell for that.

These steps will handle 99.99% of the situations in the game.

Ah, but how can you tell what protections a mage has? I belive for some of them there will be a text description in the dialogue box, but (I believe) not all the time.

I'm sure you can't quite tell from the graphics either as these are generic and show what school the spell which is being cast is from.

[img]graemlins/1ponder.gif[/img]

You can tell from the message box, unless you disabled it from the options.