Depends on the location - 5.8.4 on my desktop at home (happens to be the last time I bothered upgrading). 5.6.1 or greater at work - last year I persuaded people that we should increase the minimum supported version from 5.005 to 5.6.1..

You may be interested to know, that the last versions of HP-UX (11.0) and AIX (4.3.3) that came with older versions of perl (4 and 5.005 respectively), are currently on their way out of support. The latest versions both come with a nice shiny 5.8.x version of perl. (So we may yet jump to just supporting that)

C.