My group
Hello.
I'm DMing the module for a group of three: Dragonborn Paladin, Eladrin Warlord, Halfling Rogue.
*** Potential Spoiler Alert! ***
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I first ran them through the Kobold ruins adventure in the back of the DMG. They ran when they saw the dragon(asleep) and brought a lvl 1 Ranger with them to help kill it. They did so relatively easily, thanks to the rogue's Blinding Barrage sticking. They unloaded their Daily's plus Action points while it was blind and did a good deal of damage. Anyway, they were still level 1 after this, but I believe the first ambush of KotS got them to level 2.
So far they have only gotten through the first couple of rooms of the keep, but they have been doing ok. They had no trouble with the dragon burial site encounter, and they all survived the Irontooth fight, which can easily wipe full groups. By no means was it an easy fight, but no one died. Although when Irontooth charged into combat, attacked, Action pointed and double attacked, knocking the warlord from full hit points to single digits in one turn, it got their attention.

So far I haven't adjusted the number of creatures at all. I make the enemies use decent tactics. I don't fudge dice rolls. Oddly enough, I did note that three attacks on Irontooth exactly hit his AC, which would have been misses if the attacker was level 1 instead of 2. The biggest problem for them during the fight was the wyrmpriest, that sent two of them under after all of the other kobolds (and Irontooth) were dead. That guy doesn't miss very often, and hits pretty hard.
They're having a much harder time in the keep itself, and I'm not sure why. I play the hobgoblins a little smarter than the kobolds, always flanking, and always trying to take out the weaker armored characters first. They entered the keep fresh, and after the first encounter with just the 4 hobgoblins (and a swarm of rats that did minor damage) they burned through almost all of their healing surges on the short rest after. They had to call it a day after clearing the torture/jail room. It was eerily 3E-like. Instead of the cleric being out of spells,
everyone was out of Dailys and surges.
We press on tonight, and I intend to keep the encounters unadjusted. It's more fun when you expect to die every fight, but somehow don't. I should also note that all of my players have a ton of experience, and are getting better with each session as they learn their 4E powers.
Later!
Gruns