I have recently upgraded to Ubuntu 9.10 and found that the timeout doesn’t seem to be working.
Grub’s timeout feature allows for automatically boot up into a selected OS after a specified amount of time. By default it’s 10 seconds. For some reason this was not happening for me.
To fix it I install Start Up Manager. To do this run
$ sudo apt-get install startupmanager and go to System > Administration > StartUp Manager to get a graphical tool. It lacks a lot of options compared to writing it manually but it’s good enough. Set the timeout time and close the window. It should re-build the Grub settings before completely exiting. Restart and it should work.
Update: There was a Grub2 update between writing this post and publishing it which did change the config of Grub.