In the past, I also built several LM723 power supplies, including a switchmode one (which appeared in an Unitrode app note).
Thus, I'm also a bit nostalgic about it. Actually, quite nostalgic.
The 723 is similar to the 555 in which its ultra-simple architecture allows to be understood easily by experienced and beginner users alike. And which allows the circuit to be applied in many different ways..
That is the reason that both are still being used, and a Google search will turn up +200k hits.
The major issue it has is that it has no thermal protection for the output transistors.
Of course, being a linear regulator, it is also bulky and inefficient. And as other posters have correctly indicated, nowadays a complete SMPS will be cheaper, smaller and far more efficient.