I've got a few Canonets in my cabinet. Great compact rangefinder and in my opinion, one of the sharpest looking rangefinders. A few people will recognize it from the movie Pecker. Pretty good movie for a rained out day. If you enjoy the Canonet 28, see if you can find a good conditioned Canonet GIII QL17.
When not in use, make a habit of moving the aperture setting away from "A". It will help prevent draining the battery for the meter. Also, examine the foam around the rear film door. The light sealing foam tends to get all gummy and sticky. It is a 30min job to remove it and replace it with new foam which can be purchased from cameraseals or your local camera shop. The battery itself is also an issue. It is a mercury battery which is banned in the US. Alkaline replacements can be found at various locations including photobattery.com. If you find a canonlite flash made specific for the the canonets in working condition, consider getting it right then and there. Its a difficult flash to find and it was specifically made to couple with the canonets and their meter.
Have fun.