After an extensive search on the boards, I was surprised I couldn't find any thread about this yet. So I'm starting my own (sorry if such a thread already exists -- could you please point me there?)
I wanted to give my opinion on the new icons that will be used in the monster stat blocks, and that I've seen appear first in the PFRPG Bestiary Preview I and Pathfinder Adventure Path #25: The Bastards of Erebus.
Even though I fully support the idea of adding icons to make the stat block easier to read, I don't think DMs are waiting for icons that describe ecologies. Icons, as I see them, are an abbreviated form of some information that allows a DM to quickly assess what the monster is about. The keyword here is 'quickly' -- typically in the heat of battle (and you can take that quite literally).
Information, such as environment and monster type, is useful only when an adventure is being designed, and during the design phase, a DM has plenty of time to look over the information. Icons won't really help here. What might help in case of these ecologies, is compiling some sort of index in the back of the bestiary (or on the pfrpg-srd) where you can quickly find the monster, for example, and scan down the appropriate list. That would eliminate the need to keep flipping pages for monster types you're not looking for.
I would save the icons for more combat-related information, although I'm not sure myself what information could be used. How about whether the monster in question is more a melee, ranger, or stealthy fighter, or a mix of some of these (sort of like the monster roles from 4E, but much better)? How about icons for its most used attacks, perhaps even "linking" icons so you can quickly see which attack follows which (I'm thinking here of all the monsters that use Improved Grab first to follow it up with a Swallow Whole, for example) -- sometimes a lot of combat features can get confusing when you need to make snap judgment during combat. Or how about easily overlooked information, like regeneration, auras, immunities, or damage/spell reductions?
I realize some of these suggestions are not easily conveyed with icons, but surely there must be some better way to make use of them during the game?