No maps are needed at all. Inputting one line at a time:

$ perl -pe 's/([A-Z]+)/ucfirst(lc $1)/egi'
"THIS IS TESTING"
"This Is Testing"
"JOE MARCONES"
"Joe Marcones"
"RESIDENTIAL MAINTENANCE COMPANY"
"Residential Maintenance Company"
THIS iS a Text IN TITLE CASE
This Is A Text In Title Case
This isn't right 
This Isn'T Right 
And I'm wrong too 
And I'M Wrong Too 
e-mail is nice when capped correctly 
E-Mail Is Nice When Capped Correctly 
&c
&C
"Bit o' Mint" "Mano y Mano" "Chris diBona" "Scrooge McDuck" 
"Bit O' Mint" "Mano Y Mano" "Chris Dibona" "Scrooge Mcduck" 
"Cruella de Ville" "Jake O'Shaunessy" "Tales from the Crypt"
"Cruella De Ville" "Jake O'Shaunessy" "Tales From The Crypt"
"Sanford and Son Salvage Company"
"Sanford And Son Salvage Company"
[download]

Of course this won't and can't handle all cases. But I usually use this for small amounts of text, either to TURN OFF THE SHOUTING or to convert an all-caps title to title case, and I'm willing to correct the few errors that it leaves or produces.