[exmadscientist]

When numbering components, my favorite approach is to group designators by subcircuit. That means one circuit (say, an op-amp circuit) might have U41, R41-R46, C41-C43, and Q41; the next circuit would have U51-U52, R51-54, C51-59, and L51. You get the idea. That way, not only is PCB to schematic lookup made easy (and I find that's the one most in need of optimization), but on a good layout, a subcircuit will be laid out together, so you get PCB designator locality for free! The exception to this is decoupling capacitors; if I'm assembling by hand, I'll usually put them at the end of the list (so, continuing my previous example, they might be C60-C81, if there were only five subcircuits). I only bother with this for hand assembly, though; robots don't care.

[stephen_g]

We do things a bit like that - we break things up in the schematic by page (between one and a couple of sub-circuits per page), and then the designator is page number plus a sequential ID. So you might have C405 (4th cap on page 4) or C847, etc.

We don’t print designators on silkscreen, so it’s not really a problem with the length (e.g when you get over 10 pages and have a five or more digit long designator. With a page that is subclassed you might have one like R1208B for example!)