Call me old-fashioned, but I almost never use the following (although sometimes I use modules that do).
- source filters
- prototypes
- formats (well, that would be old-fashioned)
- tie (although it has been a helful hack for debugging in some occasions)
- attributes (including lvalue)
- barewords (not counting those that are allowed under "use strict")
- "experimental" regex features. They look cool, but I've been bitten by their bugs too many times. I was surprised to see that Damian recomends some of them as best practices!
- AUTOLOAD
- CHECK, INIT
- CORE::GLOBAL (sometimes useful, such as for testing)
- Most of the variables on perlvar, but that's too long to mention here. Many of the functions in perlfunc as well.
- <> to glob
- foreach (heh, I'm to lazy to type those extra characters. But of course I use for!)
- pseudohashes (they have been deprecated anyway)
- version strings (also deprecated)
- until
