To the review above, I would add the following three points:
1. It has the KAF2 mount.
Here's the page on Bojidar Dimitrov's Pentax K-Mount Page (the "KMP") that explains the evolution of the Pentax K mount:
Summary of the K-Mount Evolution, Names, and Features The net of Bojidar's essay is that the pinnacle of Pentax k-mount development in the film camera era was the KAF2 mount. The MZ-5/ZX-5 is a very cost effective way to get a Pentax film body with the KAF2 mount.
2. It beats the pants off my K10d as a travel camera.
One of the issues with having a nice digital camera is that you tend to baby it. It's not hard for the investment in a digital body and a nice lens to push into the $750 - $1000 range. No way around it---as a travel camera a nice digital rig is a tempting theft target. But the sleeper ZX-5? Earlier this year I took my ZX-5, an FA 50mm f1.4 lens, and several rolls of Portra NC 400 film on vacation with the family. Couldn't be happer with the results--both while I was shooting and at development time back home. Op/Tech USA makes a neoprene cover which fits the ZX-5 and a normal lens perfectly. Everything you need in one little, but stunningly effective, package.
3. The panorama mode.
There is a switch on the camera back that toggles between normal photo dimensions and panorama mode. In panorama mode, you end up with prints that are approx. 4" x 10". A very cool feature.