How to share a VirtualBox image?

Juding from your comment above, as of VirtualBox 4.0 you can copy the entire machine folder, settings, virtual hard disk and all to another physical machine (such as your co-workers), import the VM (or double click on the .vbox file) and you'll probably be ready to roll. You might have to change the network addaptor and RAM if you have different setups.

If you have a pre-4.0 release then it's simple enough to copy the .vdi virtual disk to a co-workers machine, and set up a new VM with the copied hard disk as it's primary.

The longest bit is the copying, be it to USB then to computer, or over the network, but, yes, it's fully possible.

You could use the GUI File->Export Appliance function to create an appliance and then pass the resultant .ovf and .vmdk files to your colleagues who can use the File->Import Appliance to import it.

Tombull89 and SabreWolfy, if there is ever a chance one of those images will get copied back to the source machine, the simple copy will NOT work. You will want to clone or export. VirtualBox places UUIDs into the .VDI or .VHD and will complain loudly when it finds another file with the same UUID, so loudly in fact that the guest may no longer boot. Snapshots are differences from the previous snapshot and also have UUIDs. Would not recommend VBox snapshots until you have a great deal of experience with them.