I'm surprised that people still complain three seasons into Mad Men that it's a slow show, but I suppose it'll always be a complaint people have. However, after reading dozens upon dozens of reviews of the show, as well as watching the show myself, I think it's safe to say I've learned one thing: this isn't a plot driven show. It's character-based, meaning the show isn't going to exactly going to push the plot forward every second.
This is a perfect example of the show making subtle steps forward in terms of plot but giant ones in terms of character development. Everybody had a little bit to do, including Paul, who hasn't had much to do since Season1. The scene where Paul, Peggy and the rest of the creative cast get high and come up with slogans and ideas for Bacardi Rum was priceless, and it not only gave us a chance to give Paul some screen-time but also showed that Peggy is making leaps and bounds in her quest for independence. It's odd to think she started this show as Draper's secretary and is now sitting in on meetings as (arguably) the best creative mind on the staff.
Most of the "action" in the episode takes place at Roger's house as he celebrates his impending marriage to Jane. There was plenty going on here, whether it was Pete and Trudy doing a killer dance that gained the attention of everyone in attendance (even Don seemed amused), or Don meeting up with a stranger in Roger's house and sharing a childhood story. Any time we learn something about Don, it seems like a big moment, mostly because Don is so secretive. That's probably why this scene was my favorite of the episode... a small, quiet moment that speaks so much about the character.
Speaking of quiet moments, this was an episode full of them (which is weird to think in an episode that takes place at a "soiree," in the words of Gene, Betty's father). First, there was the plot where Sally steals five dollars from her grandfather, which sends Gene into a frenzy. It may not have been overly important in the grand scheme of things but I've had a good time watching Sally Draper grow as a character, and this was a great way of advancing that arc. That quiet moment near the end of the episode where Sally gives the money back and they all sit down to dinner was beautifully done. Just as beautiful was the scene at the end, where Don and Betty walk away from Roger's party to share a moment alone, kissing passionately. I wouldn't think of Don and Betty as having a passionate relationship, but this definitely felt like a step forward for them.
The show may be slow, but it definitely isn't because of a lack of events. Things are happening, and just because they're not happening at a rapid-fire pace doesn't mean that the quality isn't good.