Using built in VNC server for KDE or Gnome I ran into several problems, like screen freeze or lost connection.

If you need a VNC server for your current desktop session in (K)Ubuntu you can use x11vnc.

1. install packages

sudo apt-get install x11vnc

2. set a password

x11vnc -storepasswd

3. start the server

x11vnc -forever -noxdamage -usepw

If you want to access your desktop via browser using a java applet you have to installa vnc-java package and use this commans:

sudo apt-get install vnc-java
x11vnc -forever -noxdamage -usepw -httpdir /usr/share/vnc-java/ -httpport 5800