I noticed in one thread on Levitation someone was calculating the movement rate with Levitation using a Magic Rating value increased by a power focus. So what all does a power focus increase a magic rating for? If you have Magic 6 and activate a rating 2 power focus do you just consider the character's Magic to be 8 for anything that uses the Magic attribute? How about Enchanting checks that use the Magic Attribute like making orichalcum?

Which rules edition are you asking about, sadly I think the answer is different for each edition.

Consider the magic rating to be 8 for anything except Focus Addiction and Magic Loss.

I am asking about SR3

In SR3 (pg. 190 of the main book), power foci increase the effective Magic attribute for determining whether Drain does stun or physical damage, and for determining the maximum spirit Force that can be conjured. Nothing else. So in third edition, an activated power focus wouldn't affect your speed when using a levitate spell, or affect your ability to create wards.

Nor your fast astral movement speed.

The advantage of using power foci or a specific spell focus when casting Levitate is that it means you are more likely to get more successes since you are throwing more dice into the test.

Quite right. (The mistakes that can occur from too many games where my int 6 all natural mage never got a chance to initiate before the game ended.)

It really is easier to just use the list of cases provided for when a power focus does change your effective magic rating (since there's only two: physical/stun drain border and maximum spirit force) rather than try to list the cases where it doesn't. However, the dice added are good for most tasks that can have specialized foci. pretty much everything a mage could want.
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Don't forget the additional dice can be used with Enchanting Tests at least according to MiTS. The Aid Power paragraph from MITS says power focus dice can be used for any magic skills test.

[QUOTE=Member #5177,Jul 6 2006, 11:02 AM]
[QUOTE=Jason Farlander, Dec 18 2003, 02:54 AM]
The "Aid Power" ability, specifically, allows the ally to function as a power focus.

As per pg. 190, SR3
[QUOTE]
You may also use a Power focus's Force dice for Sorcery, Conjuring, or Drain Resistance Tests.  Power foci dice can be used for Spell Defense.  These bonus dice may be divided up among the owner's tests each Combat Turn as desired.[/QUOTE]

So... not useable for enchanting, but useable for most other things. Just be careful when using the aid power ability in combat, especially with high initiatives -- the dice provided by the spirit will "refresh" each time you roll initiative... not each time you act.[/QUOTE]

Enchanting didn't exist until MiTS came out which was after the main book so saying the main book didn't mention it doesn't bother me. Generally I consider the later book to supercede what an earlier book says. And here is the complete sentence from the Aid Power entry from MiTS I was refering to.
MiTS pg 108
"The ally acts as a power focus, adding its Force to its master's Magic for purpose of Drain and adding its Force in dice to any of its master's Magical Skill tests each turn."

[QUOTE=Member #5177,Jul 6 2006, 11:02 AM]
[QUOTE=Lilt, Dec 12 2003, 11:17 PM]
It says specifically in the decription of enchanting that power foci dice can't be added to enchanting skill rolls.[/QUOTE]

I have looked high and low for this reference but can't find it. I would appreciate someone posting where it says that.

A Power Focus will not help Talismongering either as it is not a magical skill.

To boost your talismongery, learn botany, geology and other knowledge skills that can be used as complementary skills. Once you've got Talismongery and its complementary skills to a high enough level you're happy with, spend 1 Magic point and a few kp to make an Ally with those same knowledge skills to double your findings.