Pros
The people are AKQA's greatest strength. Yes, being an agency some of the "creatives" boggled the mind a bit, and there were occasional frictions but on the whole the team worked well. Being a techie, I was never particularly bothered by the "zomg we have such cool clients" ethos, but it was possible to work on some really interesting technical challenges using the latest technology.
Cons
The company does get a bit too pleased with itself sometimes - too many people, more the higher up you go, believe their own propaganda a bit too much. However, that's an understandable occupational hazard of working for an agency - if *they* don't believe they're the most special people in the world, how will they convince potential clients? Communication is sometimes a bit poor, and there's always been a tendency of the account management people to promise clients the moon on a stick and then refuse to listen to technical reason as to why what they've just promised is undesirable or impossible.