Adam Kennedy posted an excellent article about huge performance hits he found with File::Find::Rule. From the docs, there's this sample to find all the *.pm files in @INC: 

# Find all the .pm files in @INC
my @files = File::Find::Rule->file
->name( '*.pm' )
->in( @INC );

What this search REALLY says is "Find every single file in all these trees, then do an slow IO stat call to the operating system on every single one to work out which ones are files, and only then do a quick regex match on the file names to keep the 5% that have the ending we want and throw away the 95% that don't".

Now I'm worried about if I'm doing the right order of checking in File::Next, a lightweight file finder that ack relies on.