I still find hashes a little daunting.

BrowserUK (if I may presume) was speaking in relative terms. Hashes are quite easy compared to (for example) Perl's advanced data structures, object system, or closures.

While hashes may have a tendancy to soak up a lot of memory, it's not using it for that long.

The problem is that perl usually doesn't free the memory back to the OS until the process exits (though it will reuse that memory for other things). This is particularly a problem for mod_perl, where the process will stick around as long as Apache is up (potentially years, if your sysadmin is neglegent about security patches ;).