Is the hellfire ring bonus multiplicative as well? I think it's additive but I'm not certain.

Wyatt: Hellfire Ring is additive.

As an example. Suppose you have 35% from Hellfire Ring and 31% from a Ruby in your helm. That's a total XP bonus of 66%.

Suppose you're in a 3-player game, granting you 20% more XP (multiplicative). 1.66 (ring/ruby) * 1.20 (20% multiplayer) = 1.992

Assuming I did my math right, total bonus XP in a 3-player game with your ring + ruby: 99.2%

How come there is no "Item Hunting" tag, which means the intention to skip around all over the place to hunt elites, and farm specific areas. Not many people do "full act clears" anymore. And "questing" is akin to "full act clears" isn't it? Plus keywarden is part of Item Hunting.
So the tags would be better if they were: Questing, Item Hunting, Uber Bosses, and PvP.

Wyatt: The main concern with "Item Hunting" as a matchmaking tag is whether it actually makes it easier for multiple strangers to get around the Act quickly. As it is, everybody has a slightly different play style, route, etc. Skipping around to different locations can be worked out solo, or with a good friend, but with a stranger requires a higher level of co-ordination. Our experience is that players in Public Games often end up travelling linearly through the game because the overhead of coordinating a route erodes the efficiency gained by bouncing around that it ends up not being worth it. We really want our tags to be "Player chose tag X, therefore the expected shared activity will be Y", and for that shared activity to be unambiguously clear to all players who enter that game.
This isn't a "no" to an "Item Hunting" tag, I'm just stating our concerns. I'd say, think about it, try out Public Games on PTR, and leave us your feedback.

looking forward to trying a lot of these things out in the PTR!

Wyatt: PTR should be very soon.

Very soon eh? Might as well skip the Ask the devs part 2 and just go straight to PTR later this week or next week.

Wyatt: The Ask the devs questions right now are focused on itemization, and we know people still have itemization questions. Since 1.0.8 is focused on multiplayer, it seems like both could happen in parallel.

Thx for a response Wyatt, it's been awhile since Ask the Devs 2: Itemization Part 1 has come out, I just hope that Part 2 is coming soon, like hopefully this week. I thought it was going to come out last week, but then there was the GDC and you and some of the other developers were up North at the time I'm not sure if that is cause for the delay but it would be nice to see more of those responses, and hopefully on some of the tougher questions ;)

Wyatt: Yes - GDC was a big factor for the delay on the next round of Ask the Devs questions, sorry about that!

Any word on MOB density? Coming in this patch/ptr or moved on to the next? Great changes ahead anyway. Hope to get our hands on these much needed multiplayer improvements!

Wyatt: Yes! Mob density is 1.0.8. The blog was focused primarily on multiplayer improvements but 1.0.8 also includes increased monster density for Acts 1, 2 and 4 as well as other features such as "Craft Multiple"

No mention of Density changes, is this still in 1.0.8? Or is it pushed back or added later on to the PTR?

Wyatt: Increased density in Acts 1, 2 and 4 are in 1.0.8

Excellent additions to party play! It's going to be awesome actually wanting to play with my friends rather than feeling obligated to simply because they're my friends. Another great step.

Wyatt: Thanks! Our goal is to constantly improve the game with every patch. Personally, I play a mix of co-op and solo and definitely hear where you're coming from. I'm looking forward to the patch going live too!