To interact with VirtualBox, Veewee executes shell-commands through the 'VboxManage' command. The virtualbox gem library proved to be less stable.
To simulate the typing, Veewee uses the VBoxManage command:
$ VBoxManage controlvm 'myubuntu' keyboardputscancode <keycode>
Scancodes are injected directly from the keyboard buffer with this command. Because this buffer is small, Veewee can't type fast(er). This is why you'll notice a delay before Veewee types the commands. Speeding it up would make the keyboard buffer lose keystrokes.