The USPS still recommends addresses be entered in upper case: "We recommend that you write addresses in all uppercase letters." [1]

This apparently used to be a bigger deal back when the USPS relied on OCR more heavily for bulk mail delivery, but barcodes have become the method of choice.[2]

[1] http://faq.usps.com/eCustomer/iq/usps/request.do?create=kb%3...

[2] http://smartystreets.com/kb/faq/should-addresses-be-in-upper...

Uppercase characters are usually more reliably unambiguous when writing by hand.

With printed words, lowercase words are more legible because of the words' distinct shapes.

It seems that uppercase is just carryover from hand printing. I work with technical drawings and labels are uppercase for no reason whatsoever, and it's fatiguing to read.

... oh ya, the USPS is relevant. When did snail mail drive the modernization of anything?

Oh really? So e-commerce (which uses snail mail) is irrelevant? So the millions of products that are sold online from all over the internet just... magically teleport to their destination huh?

They don't, they just show up much better and bigger on the label.