Several people requested an update on Age of Conan, but all I can offer is some links, anecdotal evidence and opinion. From what I hear I am under the impression that Age of Conan suffers from a lack of longevity: Lots of people played it with lots of enthusiasm, and got bored pretty fast afterwards. Classy Gamer collected data on server populations, but when he pointed out the results on the official forums, Funcom censored him. And exact data on AoC subscription numbers are hard to come by, Funcom only ever posts good news, and uses weasle words like "number of units shipped" (not sold).
Of course a certain amount of decrease is due to the summer slump. But bugs and lack of endgame content certainly play a role too. Age of Conan is fun, fast, and furious. But if your're playing a female avatar, you deal less damage than a male, and the bug will take weeks to correct. If you bought AoC for the siege warfare, you found out that it simply doesn't work yet. And while AoC's storytelling and quests are absolutely great level 1 to 20, they get thinner and thinner towards level 80. Not without reason was level 1 to 20 the only part open during the beta. So it is totally possible that people cancelled their account after the initial fun subsided, and they realized AoC didn't have much long-term substance.
And then there is the alternative that players suffer from Bartleitis: "I already played Age of Conan, it was called World of Warcraft". How many people started Age of Conan for the simple reason that they were bored with WoW? But if you have been questing, and leveling, and fighting monsters for loot for 4 years and are bored of it, Age of Conan is only offering you more questing, more leveling, and more fighting monsters for loot. Age of Conan is somewhat different from WoW, especially in graphics and combat system, but it isn't completely different. Gameplay is very similar, just a bit faster during combat. If an overdose of WoW made you burn out of MMORPGs, AoC won't cure you.
So what do you think? Will everybody be back to Age of Conan after the summer, or after a couple of patches? Or was AoC just a mayfly?