I think the optimal time to upgrade something is just after the majority, so bugs have been filed, but the maintainer is still interested.
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Do users of immutable systems (i.e Nix or Guix) upgrade more or less often than other platforms?
There's less pressure to upgrade (unlike a rolling release distro) but in principle upgrading is easier.
I've had a new Linux laptop for several weeks and only just realised that I didn't have `man` installed!
Google is my default the vast majority of the time, and this seems to confirm it.
I've started keeping a list of particularly interesting bugs and patches that I've worked on: https://github.com/Wilfred/interesting-code
The time that I once removed *a single closing paren* in Emacs is still my favourite.