How can I add shortcut icon to Panel? I use Ubuntu 12.10
Unity is not Gnome and the top bar is not a gnome-panel. As far as I know there is no way to add applications there. It is only made for indicators. Applications can only be docked to the launcher on the left side (right click->Lock to Launcher).
If you don't like Unity you have some alternatives to get the Gnome2 look again. There is the MATE desktop which continues the development of the old Gnome2. I think the better choice is Cinnamon which is a Gnome3 fork. It aims to basically look like Gnome2 but with some of the benefits the new Gnome3 offers.
In my experience, sadly both don't work to well with Ubuntu. I would recommend Linux Mint, which is based on Ubuntu and comes in editions with MATE and Cinnamon.
I don't think you can add icons like you used to in Gnome 2. An icon ends up there if it's a notification. You can add icons to the Unity's dock (on the left), by right clicking on an open application's icon, and selecting "lock to launcher"
This link might be helpful: