CAPS LOCK.
Using a macro to capitalize the names of other macros where used? What crap are you on?
"Who's writing C anymore these days". Err, let's throw out the kernel, the X server, GNOME, perl, and python, shall we? All of those are written in C. As are many other things, but these are just the more popular bits.
If a key sits in your way, allow me to point you to xmodmap, or just the XKB extension. That's what it's for. Personally, on my keyboard I have mapped \ to the (totally useless) key that has ù printed on it.
Finally, a modal keyboard is useful, if only for ergonomics. Having to hold down bucky bit keys for long sequences of characters is very bad for the joints in your fingers...
This post brought to you by an inofficial member of the International Society of Caps Lock Fanciers. 7 lower case characters were hurt in the production of this entry, but no finger joints)