Turns out gksu is no longer installed by default. Some things still depend on it so it might be installed on your system - but on a clean install, it seems it's no longer required. As for why, see: Why is gksu no longer installed by default?
Historically we have used gksu a lot here but this means that in the future, we should probably scale down its use in favour of plain sudo (or sudo -i). Use the comments and answers to hammer out a best-practice if you feel there is a technical issue here.
There is a compelling argument that we move to pkexec. I just tried it here (on Kubuntu 13.04) and it worked beautifully from the terminal, a run box and from a TTY (it has a text-only mode too), but it doesn't work on a 12.04 headless server and I don't know how this works on older desktops. Comments?
###Note: I'm not suggesting an edit storm!
I am not saying we should nuke every example of gksu. Users will be prompted to install it and they can do that...
I'm only suggesting that if you're writing a new answer, you avoid gksu.
###Edit: If you need to edit something, concentrate on answers about 13.04 and newer.
In this case a quick search will work:
This query will probably return more results in time, but hopefully by posting this PSA now, we'll stop too many new answers showing incorrect information.
###And once more, if you edit, please make sure you're replacing it with the right thing.
