Question

There is no tray in Unity under Ubuntu 11.04.

How can I make icon appear somewhere in Unity? wx.TaskBarIcon is not appear anywhere.
Thanks

Answer 1

Best answer to give is from the official Documentation:

Under X Window System, the window manager must support either the
System Tray Protocol by freedesktop.org (WMs used by modern desktop
environments such as GNOME >= 2, KDE >= 3 and XFCE >= 4 all do) or the
older methods used in GNOME 1.2 and KDE 1 and 2. If it doesn’t, the
icon will appear as a toplevel window on user’s desktop.

Because not all window managers have system tray, there’s no guarantee
that wxTaskBarIcon will work correctly under X Window System and so
the applications should use it only as an optional component of their
user interface. The user should be required to explicitly enable the
taskbar icon on Unix, it shouldn’t be on by default.

http://docs.wxwidgets.org/stable/wx_wxtaskbaricon.html

So this is related to your windowmanager, not programming wxWidgets. wxTaskbarIcon is only reliable under wxMSW, dunno about mac.
Best is to avoid it if you want real XPlatform-Applications.