Have just given this another go after trying a long time ago when I was demo'ing different archiving software. It's very good but two things would make it perfect:

1) A contextual menu plugin, so you can extract archives etc all via right click. Another mac archiver, Springy, has this but I prefer BetterZip's GUI.

2) When you open a file from within an archive, edit it and save it, BetterZip should recognise this and give you the option of saving the archive with the edited file. This is pretty standard practice in most archiving software I have used. As it is you have to extract the file, edit it, then manually re-save it into the archive, which is a bit fiddly.