What are some implications of taking a break before a PhD in the US or Europe?

My perspective is primarily European, since I did my Master's in Sweden and my PhD in Germany. That said, I did take a break before starting on my PhD. It wasn't entirely voluntarily -- I did not get any PhD studentships when I wanted them, and had to wait for the next round of applications.

During my break, I moved from Sweden to Germany, and took a job doing industrial software design for a consultancy firm. It gave me good experiences, the knowledge that I could make a career in industry, and also a very strong drive to make it in academia. Furthermore, the PhD position I eventually was admitted to, I got in part because I had, at that point, both Open Source and industry experience with packaging, shipping and distributing software -- something my advisor wanted to learn more about.

For me, this all worked out well. I left my industry job after 10 months to start a PhD, I graduated with a decent enough thesis, and now -- several years later -- I am about to start the first research project with my name on the grant application.

One fundamentally important thing to note with my anecdote is that there is a huge difference in how PhDs are admitted in large parts of Europe vs. in the US. For my PhD, I applied for a job with a particular professor, which happened to include “opportunity to study for a PhD” as part of the job description. This is how it mostly is done in Germany, and also in Sweden. In this setting, it is important that you come to the PhD with a set of credentials that will be valuable to your advisor, specifically. I managed to do just this with my break -- but that was luck as much as anything else.

In the US, there seems to be a LOT more politics involved in the process, and the applying to a school aspect of the US process biases the experience more towards grooming your CV for academia in general.

Your mileage will vary.

This is, of course, ultimately up to you, people can only advise you; I will provide a list of some things to think about; hopefully this will help :)

• You say that you want to "do a good research project". Isn't that what the master's project is for? I don't know anything about unofficial projects but it could work.
• Yes, taking a break from academia would be a slight disadvantage, but if you're doing an unofficial project, then this won't be a problem at all, will it?
• "High impact research", in my opinion, is a very ambitious/risky thing to set your mind on, in terms of a master's-level project. Don't forget that as a master's student, you are still expected to be learning; a PhD supervisor is unlikely to expect something like this, although they would like it!
• Can you do a project over summer? In the UK at least, there are loads of paid internships and summer projects available, both with universities and industry.