I have a concern that if you allow the PCs to raise the spirit of Ethan Allen, they would be breaking one of the laws of Magic (I don't recall the number).  As its only a Con game, that may not be such a concern for you, but I'd hate to be a player new to the system and do something cool - like raise the spirit of a dead Revolutionary War hero - and then try to pull off something similar in a new campaign only to find out I broke the law (maybe) and the Wardens are after me to try me and execute me.

Am I remembering the Laws of Magic wrong?  And I apologize for being "that guy"...you know...the rules lawyer...

...Unless, of course, Ethan Allen wasn't actually human, and was instead an immortal of some sort from the Nevernever...then there are no problems with violating the Laws of Magic, only consequences for summoning something from the Nevernever.  Perhaps he'll need a boon from the PCs in the future in order to secure his aid?  Or at least from your NPC in case you are going to run another con game next year - continuing storyline.

This is something similar to a conversation my GM and I had.  I have a wizard from Hawaii.  My GM wanted to know how he got to the mainland since our city setting is in Dallas.  I remembered a few things from the series which seemed pertinent to the problem, and the original question.

First, this applies to the original poster's question about a room.  Mac's pub has an odd, but very specific arrangement of pillars and other items scattered throughout his bar used to unravel errant magical energies.  And Mac's is frequented by all manner of folks from the magical community with varying degrees of strength throughout the day, and it wasn't until the Dark Hallow that Mac's was without power - so unless your wizard is on par with Cowl, I don't think you'd have much to worry about if you were going to have a similar specific arrangement of 'lightning rods' in your wizard's house.

Second, Harry used a suppression spell in order to shut off his abilities (at least temporarily) in Death Masks. (Yes, it didn't work very well, but I feel that this is because shutting power off, or turning it aside is a much more delicate complex sort of magic than what Harry normally does.  He's said that he is no good with subtle magics several times)

Third, we know that running water shorts out magical abilities, also from Death Masks.

So what I came up with was a bracelet carved with runes/pictographs translating to "running water" which when empowered create a magical dampening field around my wizard.  He can't use magic at all until/unless he pulls off the bracelet.

The bracelet has yet to be approved by my GM, but it seemed as though he liked the idea.

I think devonapple has the right idea.  There's a good reason the rule books have references to libraries and time to do research.

I think there should be two levels of difficulty for lore checks.  The lower level is to know "Oh, yeah, I think I've heard of that, doesn't it have some weakness?" and the higher level is "Oh, that's an X! It's weakness is Y!".

Also, if your player is spending fate points on his lore rolls to get them super high, then he's obviously investing in knowing a lot. Let him have his fun with that.  Skill points and fate points invested in lore checks means he's not putting those resources into other areas, so you can find other ways to challenge him where he's weak.

Finally, you always have a few other options, such as splitting the party once in a while so the others don't have the benefit of his lore some of the time.  Or you could find a way to give him a compel to NOT know the answer to something.

Oh, and remember the catch rules - some weakness *aren't* known to anyone who hasn't done research (resulting in a lower catch value). Make sure you know ahead of time how much common knowledge there is about a given monster.

I like this.  There were some times that Bob was unable/very reluctant to provide information to Harry, prompting Harry to go out and do the research himself; I'm specifically thinking of Death Masks when Bob could not give any information to Harry about the , and in Dead Beat when Bob turned out to be the .

It also raises an interesting question about what resources you allow your players to access for gathering information.  Since wizards and technology don't mix, who does the research if magical means of research are temporarily unavailable?  Those individuals might not know all the correct questions to ask/locations to dig for information, and that could also lead to side adventures full of Red Herring^TM (the favored fish of GMs everywhere).

Odd thought/question:  Are all the different human mythologies encompassed in the Nevernever? 

That would account for Norse mythology rubbing shoulders with Christian mythology and Celtic mythology, , etc, etc.  Not to mention allowing for all kinds of different Scions of Power.

(For the sake of argument, lets just call what the DFRPG does with Christianity mythology.  I'm not posing this idea to start a religious debate.)

It's "Der Erlkoenig". Just because Peabody screwed up his german doesn't mean everyone has to

I was under the impression that Peabody's mistranslation of German was purposeful for the specific use of the Dark Hallow.  Perhaps I am mistaken? 

If it were up to me, changing "Der" to "Das" in his translations would allow the wizard to summon an Erlkoenig that would have none of the personality but all of the power  - no longer a "he" but an "it" - to be controlled without a will to fight against the compulsion.  Like a Fae zombie.  Now that's a scary thought.