I've been a Gentoo user on-and-off since 2004. My username, piii_man is a carryover from teenage me and a time when all I cared about was overclocking Pentium iii's, Linux HTPCs, and getting as many invites to Gmail's beta release as I could.
What initially attracted me to Gentoo was that it is source based and had a great dependency management system, Portage. In the early-mid 2000's Linux dependency management, except for Gentoo (and Debian) was really bad. Additionally, it used to be far more common to have to compile and install applications outside of the dependency manager. This was a challenge with non-source-based distributions. Often you found yourself in a dependency hell, where you couldn't compile something because you needed a library, but that library was also not available in common repositories...</recurse>. For Gentoo, this library hell was much less common; those compile time libraries, which were an afterthought on binary package based distributions, were core to the build process on Gentoo.
Now days, I like Gentoo for different reasons. First and foremost, the community is amazing. Gentoo users know their stuff. The community is smaller than most other distros, but the level of knowledge and contribution of each user far offsets our numbers.
The minimalism of Gentoo is wonderful. From USE flags, which limit dependencies pulled by a package, to the blank slate installation which doesn't even provide a windowing system out of the box, to the fact that every package you add is another package you'll need to compile, funnels your system to a place of functional minimalism.
Finally, Gentoo forces you to tinker, troubleshoot and learn more about Linux. I've learned a lot, over the years and have been able to transfer that into my career as a Scientist and part time admin of Linux based instrumentation to finally switching to the dark side (and themes), becoming a software engineer.
My personal goals for contribution to Gentoo are providing the occasional detailed bug report, helping people where I can on the forums and most importantly contributing to the Gentoo wiki. Over the years, I think the Gentoo wiki, which is still a wonderful resource, has in some places fallen out of date, particularly for systemd integration. I hope we can change that over the next couple years.