I did it during the gcc 3 transition. I used a very new gcc 3 (maybe even pre-release), which wasn't at all recommended. A couple of (most?) C++ packages didn't compile (some change having to do with namespace scope), which meant I had to fix the source of some packages (generally pretty trivial changes, usually having to prepend namespace:: to identifiers). Overall this problem was pretty rare, like it affected less than 1% of C++ files, but with things like Qt or Phoenix (or whatever Firefox was called back then), with thousands of files, I had to fix dozens of things. I guess running into problems made it more interesting and fun actually.

Did I learn anything? The main thing I learned is about all the different basic packages and what sort of binaries and libraries are included in them and why you need them. Also about some important config files in /etc. And a bit of shell experience, but I dare say I knew most of that stuff already. How much you learn depends a lot on how much you already know.

Overall what I learned was not very deep knowledge, nor was it a very time-efficient way to learn. But it was a chill learning experience, goal-oriented and motivating. And it made me more comfortable and confident in my ability to figure out and fix stuff.

Also it's obviously not practical to keep that up to date, so I switched back to a distro after a couple of months of this.