like the KML/KMZ format. Of course applications will need to read/write this format directly, without the user zipping/unzipping.
Rationale: I see many casual users confused by the concept of a shapefile consisting of multiple files, and when passing on shapefiles by email or upoloading to AGOL (a) they curently have to zip/unzip manualy and (b) tend to forget some bits. A SHZ format would make these things much more straightforward for users.
I am aware that reading/writing into zipped files does impact on performance, but the KMZ format shows that it can be done.