AndyC, for your example of CLK_25M/Clk_25M/clk_25m, it'd be just as easy to not notice that there are multiple different nets named CLK_25M/CK_25M/CLK_25, etc. It might be noticeable here since they're written side by side, but in practice I wouldn't notice unless it was something I was specifically looking for. If it were actually intentional that these be different nets, I personally find CLK_25M and clk_25m easier to distinguish than any of the all uppercase alternatives. Maybe one is a global net and the other is local...it could actually be useful. Really though, these should have more descriptive names if they're meant to be different nets.
For your example of CANL_IO1, I want to clarify I'm not advocating for all lowercase as the alternative to ALL CAPS, but instead mixed case (i.e. allowing, not requiring lowercase). For CANL_IO1, I'm assuming CAN is an abbreviation for controller area network, L is an abbreviation for low, and IO is input/output. These all make sense capitalized, and I would still write these as all upper case on a mixed-case schematic. I'm not saying we should all go out and convert everything in every schematic from all uppercase to all lowercase.
What's hard to read (i.e. slow and easy to misread) is a lot of net names and pin names are clearly just words or multiple words (possibly separated by an underscore, but also a lot of times in practice just run together) mixed arbitrarily with initialisms and abbreviations, and run together as one continuous uppercase "word" with no clear boundaries between words/initialisms/abbreviations. I can go back to old schematics that I used to look at daily, and it's still easy to initially misread these names or have to spend extra time parsing out the boundary between words/abbreviations/initialisms when everything is just one long uppercase "word". Even worse is when a long list of these names are all uppercase and also very similar to each other and right next to each other.
With regards to your comment "I don't care whether or not you *like* reading..", it's not just about what I like. You act as if using all uppercase somehow magically makes all ambiguities go away. And that's not true. There are quite a few ambiguities with ALL CAPS also (more than lowercase, where the main ambiguity is between 1 and l): compare I1 vs i1, EF vs ef, PR vs pr, Z2 vs z2, S5 vs s5, CG vs cg, B8 vs b8. In Mentor Graphics tools, where the default stroke font is a slab serif there are even more: compare HA vs ha, 7T vs 7t, IT vs it. At extremely small font sizes, and after photocopying these ambiguities get worse. There is less variation between uppercase characters as a whole.
https://en.wikipedia.org/wiki/All_caps#Readabilityhttps://en.wikipedia.org/wiki/All_caps#AmbiguitiesI don't take a magnifying glass to individual net names, and empirically it's far more common to mistake different uppercase letters and numbers when scanning a document than I've ever had for lower/mixed case text.
For PCB drill drawings, if you mean just the drill charts showing where the different kinds of drill holes are, I don't mind all uppercase symbols. Or even just circles, squares, triangles, x, +, and random other symbols are pretty common and get the job done. These aren't something you read.
If by PCB drill drawings you mean entire PCB fab drawings with notes, then yes you're right in saying that I probably wouldn't like reading them if they're done in ALL CAPS, especially the notes. I can understand the argument for net names more, but there's no reason for actual text that you have to read to be in ALL CAPS. It's not an issue of it being "shouty" either, since it's pretty standard and I'm used to it, it's an issue of legibility. Can you show me an actual list of fab notes that you think would be clearer written completely in ALL CAPS as opposed to mixed case?