I finally managed to get it to work. All I needed to do it go to /etc/default/acpi-support and set DOUBLE_CONSOLE_SWITCH to true. Now I can resume from standby in Ubuntu 10.04. For now I've only done this on my test system, but soon I will upgrade the main system - finally.
Update: Actually it's still a bit buggy then. I still get a blue flickering after resume until I manually switch to X with Alt-F7 and back a few times.