Because the Net::Z3950 code is driven by the standard generic event loop (provided by the Event module), you might think it would be easy to integrate it with with a GUI toolkit to achieve a GUI Z39.50 client. Yes and no. The two main GUI toolkits for perl are Tk and Qt: the former does not integrate with Event, but the latter does - although I've not done it myself. See the file perlqt.t in the Event distribution, which shows how to do it, but hints that it will probably be necessary to rebuild Qt first :-(
Looks like I'm going to have to either learn Qt <sigh> or wait until the Tk maintainers fulfil what's apparently a long-standing intention to make it Event-friendly <double-sigh>