This guide is obsoleted. Please refer to this one instead.
at last i've figured out a way to do this. there are still some glitches / shortcomings though, but i'm hoping to smooth those out with the responses to this thread. [EDIT: The 0.60-1 version of Alltray has a --sticky option which makes the target application appear on all workspaces, so we no longer need devilspie or any other window matching function.]
1) download and install alltray.
2) set up a new profile in gnome-terminal. i'll call the profile name "tterm" here, you call it whatever you fancy. edit the profile with the following options: uncheck the "show menubar by default in new terminals" option in the "general" tab, in the "effects" tab choose "transparent background" and set transparency level as you like, and in the "scrolling" tab, disable the scrollbar.
3) create a launcher with the following command:
theoretically you can add a --geometry option to the line to determine where the window will pop up, but i haven't got this to work. maybe it's an alltray issue; gnome-terminal just won't obey my orders while launching with alltray. if you want to fiddle with this you can find the x window server geometry specification in the manpage for x; i find it easier to just move the window to wherever i want it to stay, since it has to be done just once per session.Code:alltray --borderless --sticky "gnome-terminal --window-with-profile=tterm"
4) double click the launcher, position the window, click the tray icon, and viola.
[EDIT: The below section is outdated and I'm keeping it here for the sake of not losing context in the replies. It's safe to ignore.]
now my major complaint with this method: i just can't get devilspie to hide gnome-terminal from the task list and workspace pager, and put it in all workspaces. in short devilspie won't recognize gnome-terminal at all with neither the window_title nor the application_name properties. i've tried setting different titles, without luck. maybe this has something to do with the "(AllTray)" suffix added by alltray?
this is not a biggie though, because this method is meant to provide a pop-up terminal, and since the tray icon is always fixed on the panel there's no real need to make it appear in all workspaces. and the task list item only appears when the terminal is up, so it doesn't take up space all the time. so, not to get bugged by these issues, close down the terminal when you're done with it, and open it again when you need it; it just takes a click
hope you find this useful. and devilspie hackers: help me sort the minor quirk out!