FSVO front end, Objective C and Cocoa (presuming the constraint of said front end residing only on OS X was acceptable :).

For something more cross-platform, MacromediaAdobe's Flex toolkit is pretty neat. Using it for some reporting stuff (the free compiler along with the for-pay charting and graphing components) at $work and it's not that bad (once you get over the fact that you're writing strongly typed Javascript (of a sort)).

And in both cases there's XML and JSON output generators that can be POST'd to a backend web server using whatever Perl framework you want.

More thoughts: Alternately in the ObjC case you could just write to flat files or an sqlite DB and pass things back and forth that way. Or use CamelBones and have your perl run as part of the front end itself (don't know offhand what the status of CamelBones on Leopard is though . . .).