I used to use an Ikon, went through all kinds of M, Hexar, CLE and Bessas after it, and bought one back last year. It's an extraordinary tool which just shoot away, which suits my style.
If you wanna shoot and prize speed and ease of use, get it. If you worry about the extra weight a pair of spare LR44 bring or how your tool will be like after a decade of hard use, think otherwise.
In fact it's not all that hard to service since the ZI is quite a simple camera. Not as advanced (which means trouble) like a Hexar RF, it has just the "right" amount of technology. RF calibration is doable (there's a tutorial somewhere once you google it) and electronics is OK, it's as reliable as a Nikon F3. Cosina as a company is doing pretty good and will provide backup for more complicated issues in the forseeable future.
I still keep my M for fun.