Pros
This is one of the best places I have ever worked. The team is very smart, most of the people I work with are problem solvers and it's not hard to get answers to questions because that's what they do. Everyone is focused on making things happen, so things happen quickly and I find that exciting. You learn new things. I have gone from backend development to front end development to light project management to leading sprints and back to each of those roles. It's nice not being stuck in the same position and knowing I can talk to a PM to take over on something I find want to learn. Besides the on-the-job learning, you get to go to Drupalcon at least once a year (sometimes more.) Everyone seems to know who Trellon is and that our team is smart and has been around a long time. You get to go to other events as well, and management supports things going on all over the world. You work with awesome clients. They mostly are non-profits who are doing good in the world and you get to think about really awesome issues. Most of the people I work with care about open source as well and understand things like sprints, technical debt, repositories, deployments, etc. I don't spend a lot of time educating them on the fundamentals of what we do.
Cons
There's a strong culture here that is not for everyone. There's no good way to send the message when someone is not working out. Management is not really tuned into when someone is not getting it, or the problems it causes, until it's too late. This means people sometimes leave on bad terms and people are scrambling to clean up the mess they left. You have days when you spend most of your time explaining things to others that they should already know. It's nice when they learn and make your job easier, but it doesn't always happen. You have these moments when you realize you spent 2 hours explaining something that would have taken you 5 minutes to do. You can set your own schedule, as long as you stick to it. Not everyone does, I don't like wasting 15 minutes for someone to get back from buying tacos. The CEO is not as bad as other people claim, but he is really into politics. I don't talk about politics with him because he can't stop. Otherwise, he is about as competent / inspiring as other people I have known in the same role.