I started a Ztool at work with a timelapse recording to show my WIP and ended up wanting to bring it home to work on it some more. I was going to email both the ZTool and the ZMovie home but my ZMovie ended up being something like 54MB; too large to send over gmail.
Is there a way to append (add one zmovie on to the end of another zmovie) or am I doomed to have to wait 'til tomorrow to continue my work?
You should be able to use Movie>Load Movie to bring it back into ZBrush. Then click the Record button. It’s tooltip says “Begin/Resume Recording”, so it’s a pretty good guess that you’ll be able to continue. 
I do recommend saving under a new file name when you finish. And it’s probably a good idea to export a QuickTime before you close ZBrush. Large movie files can become a problem to load sometimes, and it would suck to lose your work.
Also keep in mind that with QuickTime Pro you can do a lot, such as breaking movies into smaller parts, etc.
Yes, I realize that you can continue recording after you load in a file… but can I take a ZMV file and add it to the end of another one? For instance, if I record a movie at work, save the movie file & email the ZTool home, then come home continue working and record a completely different movie, then go back to work and append the movie I recorded at home to the end of the movie I made at work?
Or do I need to write out the .MOV files and append/combine them in an external editor?
You’ll need to write out the MOV files. There’s not a way to splice ZMV files together.
Ah ok…
Maybe in Z4?