UPDATE I still enjoy Metalsmith. But, as of right now it's not part of my build. I was able to get the same functionality using my own doloop npm module.
Building this website was my first time using Metalsmith, and I must say... I really like it! I think there are a few things that I need to improve in my flow (like the file watchers -- currently I have to stop Node and restart to rebuild when a collection template or post changes; all other file changes are watched and rebuilt properly).
There has been a few headaches though, namely Metalsmith Collections and working with the underlying data that gets created. But, for the most part it's been a fun and smooth web building experience and it's helped me get better at tooling and project workflow. My existing workflow was a simple gulpfile, and while this is similar, I believe Metalsmith is much more versatile and useful.
I especially love the fact that I can add a simple HTML file that is tagged as a blog post or portfolio post, and the site rebuilds and takes care of itself to link assets together.
I hope to be making another blog post about using Metalsmith with more in-depth techincal discussions. Stay tuned.