The most important thing to know about IPA is that they have champagne taste but offer beer salaries. They tend to only hire candidates from top notch schools, e.g., Harvard and Yale, and even require staff to hold MAs for entry-level positions. Regardless of your pedigree, the pay is terrible...even relative to other nonprofits. In the US, which includes the New Haven, DC, and New York offices, you should expect to make around $42K (or less) as a research associate, $49K as a coordinator, and $56K as a manager. If you are carrying significant debt from graduate/undergraduate school, it is hard to make ends meet on such a low salary. It is for that reason that most of the people who work there come from wealthy backgrounds, and their parents subsidize their living expenses and/or paid for their university.
While the people who work at IPA are fantastic, the professors who lead on our rigorous academic research gravitate towards studies that lack policy relevance and increase their chance of getting tenure. This can be frustrating for staff and implementing partner organizations. In addition, the professors (or PIs) can be a bit hard to work with, and one has to learn to manage up as an IPA staffer.
Similarly, you will need to learn how to deal with incompetent middle and upper management, which is ineffective, poorly trained, and unprofessional. It is imperative that IPA starts hiring managers that know how to delegate and manage people. What is happening now is IPA hires or promotes managers that are technically strong but have no idea how to work on a team or manage a team. I do think IPA's poor managers are one of the core reasons for its high turnover in the US and field offices.