I wouldn't take it myself, you are better off using slots to enhance your other powers.
I take it instead of any of the Fighting pool. For the vast majority of scenarios Tough and/or Weave are overkill in terms of Willpower survivability for me, so I save a slot or two and just get Strength of Will for when things look a bit hairy.
I don't think of it as a panic button, it's not that kind of power. I size up a situation and decide I'm going to use Strength of Will before charging in.
Chairman of the Charity of Pain; accepting donations of blood and guts.
Prophet of the Creamy Truth; "If it's empty, fill it with cream."
same as khorak - i tun it on when i feel i need it - or hell - even if i just feel likeit, its not a long cooldown, and ill be using it along with tough (coming at 47) to nearly cap myself for smashing / lethal resists, and hell it onyl needs 1 extra slot so you have 2 resists in it - seeing as 2 slots soft caps the resists for anything (or defence - and regen really to) compared to needing 3 more slots for tough (2 end reduction / 2 resists) its pretty economical not to mention it makes you even stronger vs psi hehe so should be a popular secondry for pvp come the influx of psi blasters lol
I got it, its nice to be honest. It's one power and one slot with two dam resist in it. Doesnt need more. On my recently dinged with no sets ss/wp brute it means that I can suddenly solo the 8 man nemesis spawns on battle for tv. I need one to help if I dont have SoW running.. So for me thats a 100% increase in effeciency 2 out of 5 minutes 
I run tough too in case you wondered.
Since you're not capped in S/L resists with Tough it'd be nice to have. I'd take it.
As I creep up in levels to the point where I have planned taking Strength of Will, I'm getting more and more dubious about whether it's a good pinnacle.
Hell, that's too kind, I'm getting dubious whether or not to just ditch it for something else, really.
<ul type="square">[*]Yes, it makes you practically unmezzable, but I've never actually had Indomitable Will fail me yet.[*]Sure it gives you *booming voice* MOAR RECOVERY but Quick Recovery and Stamina isn't already enough?[*]Slotted it gives you S/L resist, and far, far less resist to everything else.[*]Now, assuming you're taking weave to wrench up your defenses (I certainly am) you're already getting tough. Do I really need more S/L resist?[*]On the other hand, the 15 or so percent of resist to everything else certainly won't save me when I really really need it. Think enemies like, say, Positron Automaton which hits you with energy that decreases your defense. 20% instead of 6% resist isn't gonna save me from him.[*]Can't even slot it for recharge like everyone else can. Or use hasten on it. Or anything.[/list]Is this just the most disappointing damage mitigation ultimate ever, or am I seriously missing something here?