Actually, you'd be surprised what adrenaline does to people. A fight can make people lose all rationality--they may not turn into zombies, but someone who's pissed off enough to start swinging at you probably isn't going to care much about what you're saying right at that moment.

I agree with this.  My personal interpretation, though, is that there's more to social attacks than just what you're saying - it's also about your body language and personal presence.   An Intimidation roll could easily be about looming over someone, making a sudden, threatening motion, or otherwise acting in a way that makes your opponent react as though you're a credible threat.  An opponent hopped up on adrenaline will still respond to those kinds of signals - it's communication on a more basic level.

In the end, it really comes down to GM discretion and what makes sense in the situation.

I've done this as a social character before, but the GM has mostly handled it as me using my social skills to create blocks against creatures attacking rather than straight up social combat.  My 2 cents is that it depends on the situation - is the Ogre going to listen to the Supermodel?  Or is it too busy fighting the other party members to pay much attention to what she's saying?  If it's in a blind rage, furiously pummeling everyone before it, it's probably not paying enough attention for her to get through to it.  But if she gets its attention, or there's a lull in the combat, it seems like it should be possible to roll social attacks against it.

My favorite is "If it's stupid and it works..."

It gets me into and out of some very fun situations.

Hi, Jeff! *waves*

I'm new to the DFRPG myself, but most of my concerns would be the same ones you'd have in any chat environment. The biggest concern I have for any chat game is continuity and communication between GMs.  If you're going to have multiple GMs running plots at the same time, it'll be really important for all of them to communicate what the potential consequences of those plots are so they don't step on each others' toes.

Specific to the DFRPG, how would you handle milestones?  Chat sites for other systems tend to hand out a certain amount of XP each week, but advancement in the DFRPG is based on story milestones.  And, on a chat RPG like the one you're describing, not every character is going to experience stories at the same rate - some might never even get into a GMed scene at all!

My recommendation would be to make significant and major milestones chatwide - raise the skill and refresh levels for the entire chat at once, including new characters created after the milestones.  Maybe make them coincide with big metaplot events.  Especially in a system like the DFRPG, where a single skill point or point of refresh makes a huge difference, I think the game works better if all the PCs are on equal footing.

Also, you're going to want to have a clear policy about how magic items and crafting works.  I'm not actually familiar with these rules, but the discussions I've seen here give me the impression there's a lot of room for different interpretations of the RAW.