GNOME will detect an iPhone or iPod Touch as a camera, and ask you if you want to import pictures every time it’s plugged in.
The Always perform this action doesn’t work for ignoring the dialog, so how can you stop it from being trigged whenever you plug in your iPod? Open System->Preferences->Removable Drives and Media. Under the heading for digital cameras, deselect the option for importing digital photos.
Of course, you can change behavior for many different devices in this dialog. If you’ve got another device, there are even more options available: open the file browser, click Edit->Preferences, and select the Media tab.