Some observations based on personal experience last night:
The system makes a lot of sense if you think of initiative as time units. Each round seems to be considered 6 seconds (Arcane Cleansing went from 999s to 167 rounds). Each point of initiative seems to be one second, roughly (Chill Fog has a cast of 4.5 in turn based and 4.5s cast time in real time afaik).
Fractional initiative seems to count for determining acting order, but is otherwise rounded up.
A round ends when all actors have taken their action. You can delay your actions as long as you haven't done anything, and it will put your character at the very end of the round (first in, first out). Delaying basically sets your initiative to LAST_ACTOR_INITIATIVE + 1
How casting works: the spell will take effect at CASTER_INITIATIVE + CAST_TIME. Rounds are not delayed by casting. Example: Watcher with initiative of 6 casts Chill Fog (Cast time of 4.5) with no action speed bonuses. Spell should go off at initiative value 11 (6 + 4.5 = 10.5, rounded up). If someone would act at an initiative value higher than that, it means the spell will fire the same round. Otherwise it gets pushed to the next round. If the last actor acted at an initiative value of, say, 10, the Watcher's Chill Fog will go off at initiative value 1 in the next round.
Base initiative is 6, modified by armor initiative penalty, dex and action speed. Stealth provides -85% initiative. Starting a fight from stealth pretty much assures you to act first in the first round of the fight. Subsequent initiative depends on what actions you take. Using a weapon/spell will put you at whatever initiative that weapon/spell has. Not taking any action puts you at initiative 0. I still haven't figured how to dash (trade action for extra movement).
Effect duration: they seem to have taken real time ability duration and divided by 6. For instance, a Monk's Swift Strikes will last 2 rounds once you get about +20% duration from Int and PL (from 10s real time duration to 12). This seems to round down.