Nice to find an article talking about how to deal with vnc4server on Xubuntu, especially for auto startup. With my imagination, now it's for Ubuntu use as well;>
Making vnc4server start automatically
You can make your vnc4server start automatically with a simple one-line script.
Paste the following into the script editing the resolution to your liking:
Now save the file and exit nano. You'll also need to make the file an executable, do so with the following command:
Finally, to have this script run automatically, simply add it to your startup group:
To remove it from your startup list, do this:
For Gnome user, better do this: