The Celtic's Pub is one of the few places where you can get a Guinness in Mexico(although not on tap). There is another one in Col. Condesa that has been around for a bit longer but is essentially the same as the one in Polanco. It's location in the hotel zone (right in front of the W) makes it one of the hippest places to be seen.
As with any other pub in Polanco, this place is always busy, no matter what day of the week. We had trouble finding a space at 7pm on Friday, and when we left at 10:30pm, you could hardly move around.
The crowd is notably upscale with an average age in the mid-30s. There are about 20 tables of varying sizes, a few couches and a coin-operated pool table.
The food and drinks are reasonably priced, and the waiters are extremely attentive and fast to respond. It gets a bit loud once the DJ starts playing music at around 9pm, which makes it almost impossible to converse. Most people come in groups, so don't expect to meet a lot of new people here. All in all, it’s not a bad place to have a few drinks and unwind after work.
One final note is that the valets are slow in returning your car. It will usually take 10 minutes, and sometimes as much as 15 minutes.
Beer: 30 Pesos
Guinness: ~60 Pesos
Appetizers: ~70 Pesos