I'm sure that you've closely examined all of the Main Menus on the back of the D90. They are all laid out there in sequence top to bottom: Playback Menu, Shooting Menu, Custom Setting Menu, Setup Menu, Retouch Menu and toward the bottom is the Recent Settings Menu. But there are sub-menus buried under sub-menus (some I am sure I have never found) so if you haven't discovered the My Menu, don't feel like you are The Lone Ranger.
My Menu is where you can save other menu settings that you use and might need to change frequently. By saving them in My Menu, you don't have to click and scroll from one main menu to another and then to a sub-menu and another sub-menu - and on and on.
Go to the Recent Settings/My Menu on the left (the bottom main menu above the question mark). When you click it will show all of your recent changes to all of the menus. Hidden at the bottom of the list is Choose Tab. If you select Choose Tab and click OK, you will see My Menu and click on it. Now you have your own personal menu where you can add the settings that you need to access or change most often. At this point, you can click on Add Items which will bring up the five main menus and allow you to go to the sub-menus and add your settings to your list. Once you add a few items you can change the order in which they are listed or remove something if you decide in the future that it isn't as important as you once thought.
Now, just when you think life with your D90 couldn't get any better - if you find yourself using your My Menu often, try reassigning a designated button on your D90 to take you directly to My Menu so you can access your selected settings quickly. I reassigned my FN button which I wasn't using (found on the right front under the autofocus assist light) so that when I push the FN button, the first item on My Menu list pops up on the screen. You can reassign the FN button or one of several other buttons by going to the Custom Settings menu / Controls sub-menu and find Assign FUNC button (or one of the other buttons you don't use) and find Access Top Item on My Menu and click OK. Now every time you push your designated button, My Menu will pop up and you can scroll backwards through My Menu to other items you have saved as important.
I have AF-Area Mode as my first assigned item so I can change it quickly without searching. Among other selections, I also have Assign AE-L/AF-L button, Focus Point Wrap Around and Battery Info on My Menu.
Take a look and give My Menu a try and tell us what you put on your My Menu. I think once you use it you will be glad you found out about it.
Witten by BayDogs