R. John Shields wrote an interesting piece about his experiences with m2eclipse. He compares Maven support in m2eclipse and IDEA, and he gives an honest appraisal of what he considers to be gaps in both products. In general, he appears to have had a generally positive interaction with m2eclipse, and this is exactly the kind of good natured, honest, and constructive feedback that Sonatype can use to cycle back into its project evaluations and requirements. Here's a excerpt of his post in which he comments on something that Sonatype's developers feel strongly about, that is the idea that the Maven POM be be treated as the one, "source of truth" for a project.
What you really need to know is that using m2eclipse on your project tightly integrates Maven with Eclipse. Maven’s POM is the “source of truth” for your project. In other words, your POM is your project file. In fact, I’d recommend that the Eclipse .classpath (and maybe even the .project file) not be checked into a source code control system. Its replaced every time you make a change to your POM. This is important on my current project where I have several different profiles for running on different application servers and/or running with all local or shared resources. All I do is change my active profile and my source folders will be reset accordingly (picking up the correct *.properties files, Spring configuration files, etc).