[dolmen]

+1

This would allow to avoid space, %, / and + to be more URL friendly, and so allow more usages.

[kristov]

Having these chars is a pain (particularly space). Manipulating lists of these in files with standard Unix tools will mean having to escape, quote, etc.

[mr_mitm]

I don't understand why they didn't use lower case letters instead of special characters. Does anyone here know?

[lifthrasiir]

You can't put lowercase letters in the alphanumeric mode (5.5 bits per character) and need to switch to less efficient byte mode (8 bits per character).