I'm running Age of Worms as a gestalt campaign in Greyhawk. I used Whispering Cairn almost straight out of the box, but The Three Faces of Evil is modified heavily - I like all of my changes, which focused on eliminating 'mobs' of weak enemies and replacing them with fewer, more powerful enemies. In the case of the Vecna temple, I eliminated all of the original labrynth denizens and replaced them with a 10 HD half-fiend gauth beholder. It was a challenging (and frustrating) fight, since the beholder was able to use Flyby Attack to dart from one hidden passageway to another, blasting the party with eye rays midflight before disappearing from view.
But the beholder encounter was just a taste of what was waiting for them in the Inner Sanctum. For reference, here's my party lineup:
Kellen - ninja/cleric of Nola 5 // ninja/shadowbane stalker 1
Khalavas - barbarian/bard 5 // dragon disciple/war chanter 1
Quince - wizard/warmage 6
Darion - fighter/knight 4 (party cohort)
I made the Faceless One a necromancer/cleric of Vecna 8; I kept the allip the same, but raised the acolytes to 3rd level and made them sorcerer/wizards.
When they arrived in the Inner Sanctum, the Faceless One had fly, greater invisibility, mirror image and a host of other buffs active. He hit Kellen with a bestow curse (Kellen failed his Will save) and picked the '50% chance to act' option. One acolyte cast web and the other cast glitterdust - Kellen failed his save vs. the web and became rooted to the ground. Everyone else succeeded their save vs. the web and the glitterdust, and were merely entangled. This still put them in a rough position, which the Faceless One capitalized on by blanketing the area of the web in a stinking cloud (Quince failed his save and became nauseated). The allip showed up at the same time and entered the area of both spells without any difficulty. All of the PCs made their saves against its babble, but it still managed to drain some Wisdom from Khalavas before Kellen was able to destroy it with a greater turning.
Things got pretty bad after this; all of the PCs started failing saves or Strength checks to get out of the web and stinking cloud, but they had total cover and total concealment from the Vecna mages on the other side. The Faceless One put the hurt on Darion and Khalavas with an empowered lightning bolt, but quickly ran out of damaging area effect spells. The acolyte who cast web dismissed it so they could finish the PCs off, but the PCs started running at this point, egged on by a potent casting of fear from the Faceless One. Khalavas failed his save vs. fear, and since he was the only one in the group who hadn't been nauseated by this point, he was able to outrun them by a good distance, darting through the labrynth and out into the Dark Cathedral.
Being the wicked DM that I am, I decided that the Faceless One would take his acolytes with him via dimension door to the Dark Cathedral to cut the PCs off. When Khalavas arrived a few rounds ahead of his party in the Cathedral, he found the Vecna mages waiting for him. They all cast charm person simultaneously - he was able to shake off all but the Faceless One's casting. They had a battle of opposed Charisma checks at this point as the FO tried to convince him that his friends had betrayed him and left him for dead. In the end, the FO only managed to get him to agree to stand aside and watch the battle.
Luckily, when the rest of the PCs arrived in the Cathedral, Kellen opened up with an area dispel magic, which knocked out some of the Vecna mages' buffs, but more importantly dismissed the charm person on Khalavas. Battle was resumed - the acolytes managed to take out both Quince and Khalavas with hideous laughter and Darion was brought into the negatives by various direct damage necromancies delivered via ghost touch (inflict serious wounds, vampiric touch, chill touch, etc.)
This left Kellen (who was using ghost step to remain unseen) to manage the battle as best he could while the hideous laughters wore off. It was a pretty close thing, but the acolytes were down to their cantrips. The Faceless One tried to murder Khalavas with a phantasmal killer, but he made his save. Once Quince and Khalavas were back up the battle ended fairly quickly in the PCs' favor.
The best part of this was that the PCs got to witness the Ebon Aspect's 'birth'. They are extremely tapped on spells and resources (Darion is still down) and the Aspect is seriously bolstered (I made it a 14 HD Ebon Aspect and gave it light flails for its three functional claws to wield), so I gave them a short reprieve. The Aspect left the Dark Cathedral, compelled by the nature of its birth to an act of vengeance beyond simply killing the temple intruders. The PCs will no doubt rest before they track him back to Diamond Lake, where he has begun destroying the temples of Heironeous and Saint Cuthbert. If they don't intervene, he'll raze the town in a day or so. Allustan is currently on a delve in the recently cleared Whispering Cairn, so he isn't around to aid them. Besides, the PCs (as a group) are much more powerful than him at this point.
A side effect of all of this is that Filge (who is currently being held prisoner at the church of Heironeous) will be able to escape during the pandemonium. I love recurring villains...