It will affect the -Def and the -ToHit whenever the PB is active. the best way is to toggle then PB so you don't waste time in animation.
(QR)
Power Boost works by increasing the (de)buff of other powers for either:
A) The duration of PB if the other power's duration is shorter
or
B) The duration of the other power if it is longer that PB's
For toggles, you need to remember that they are not static effects. Toggles are actually very short duration (2s at the most, usually much shorter) powers that are constantly reapplied for as long as the toggle is active. That being the case, a Power Boosted Radiation Infection would only last 15.5s at the most (15s for PB, .5s for RadInfect's refresh rate).
So it's not worth it to try and PB toggles in most cases. Save it up for long duration effects (such as Vengeance).
Head of TRICK, the all Trick Arrow and Traps SG
Part of the Repeat Offenders
Still waiting for his Official BackAlleyBrawler No-Prize
I suggest PBU with:
Lingering radiation
EM Pulse
Accelerated Metabolism
Triumphant Defenders Forever
Psylenz FF/Psi, ArticQuark Storm/Rad, Symon BarSisyphus Bots/psn, Max VanSydow Thugs/Dk, Cyclone Symon Bots/stm, Blue Loki Ice/Cd, Widow 46526
HelinCarnate:OMG it is so terrible. I have the option to take 3 more powers but no additional slots. Boo F'ing hoo.
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I suggest PBU with:
Lingering radiation
EM Pulse
Accelerated Metabolism
[/ QUOTE ]
Of those, I'd only use it with EMP.
PB doesn't affect Regen, Rech, or Recov.
If you used PB with Lingering Rad, you'd only increase the -RunSpeed.
With AM, all it would boost is the +RunSpeed. Possibly the Mez Resist as well, but still not very notable.
With EMP, you'd get a Hold that lasts around 50s. Now that's an emergency button.
Head of TRICK, the all Trick Arrow and Traps SG
Part of the Repeat Offenders
Still waiting for his Official BackAlleyBrawler No-Prize
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With EMP, you'd get a Hold that lasts around 50s. Now that's an emergency button.
[/ QUOTE ]
On top of some VERY good -endo 
Hmm...come to think of it...I wonder which Primary and Secondary powers benifit the most from Power Boost for a Corruptor in the first place?
I could look into it, but does anyone have any insight to shoot out off hand?
Last I heard the /Cold shields don't benefit from PB. Is that still the case?
What about Frostwork?
Cold loves power boost because of benumb.
The cold shields don't benefit from Power Boost because they have a +resist portion (cold, fire). I'm not sure about Frostworks but I wouldn't have thought so. That's because its not a heal and a +hp like Dull Pain, its just +hp. In addition to that it has a +resist portion (toxic) so I doubt it would work anyway with PB.
Support Guides for all Corruptor secondaries and Fortunatas
The Melee Teaming Guide for Melee Mans
The Melee Teaming Guide for Melee Mans
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If you used PB with Lingering Rad, you'd only increase the -RunSpeed.
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I love Power Boost, I keep finding new ways to use it. 
Soak an alpha? PB->RI (ensures the tohit debuff is enhanced for the first volley)
Heal up fast? PB->RA->Life Drain
Stun a lot of minions for a long time? PB->Dark Pit
Hold something for a long time? PB->Soul Storm
Hold a lot of things for a long time? PB->EM Pulse
Fast vertical travel? PB+GvE Jump Pack+Raptor Pack [edit: My Corruptor is a Super Speeder]
Misc stuff? PB+AM / PB+LR
[edit: Need extra tohit? PB->Soul Drain]
[edit: Extra long immobolize? PB->Tenebrous Tentacles]
Power Boost is my awesome button. If I ever finish my build (I'm dragging my feet because it's so freaking expensive) I'll have it recharging every 35s. 
[ QUOTE ]
Hmm...come to think of it...I wonder which Primary and Secondary powers benifit the most from Power Boost for a Corruptor in the first place?
I could look into it, but does anyone have any insight to shoot out off hand?
[/ QUOTE ]
Rad/Dark
I'd say Dark/Storm would benefit very much as well.
So, i'm curious. Will Power Boost affect toggles such as RadInfec and Enervating Field that are already toggled on an enemy or would you have to Power Boost and then throw the toggles onto the enemy?