One way that I've done this kind of thing in the past is to really use
SSI and call a mod_perl handler or Registry script with it. In other
words, you write a "list users logged in" thing in CGI::Application as
usual and then call it like this from a page:
<!--#include virtual="/perl/users?rm=list&max=5" -->
That just makes an Apache subrequest and is very efficient.
If what you want is a bunch of little "portlet" widgets, this can be a
good way to do it.
Dire warning from bitter experience. If your little portlet widget
does something slow, your whole page will be suitably slowed.
(We used to insert banner ads, using a less-than-optimal ad selection
engine, this way. For this., IFRAMEs are the way forward - or for
that matter client-side JS).
