Manage Applications > click on your app that want moved to usb storage then click Move to usb storage. Simple no rot needed absolutely built into android 2.3
Again, still there are some apps in which that "Move to usb storage" button is not enabled, and they are not stock apps. I have pointed an example, a game called Clink. Find it in Market, install it and try to move it yourself to find out what happens.
There is 16gb's total space you have to use how is that not enough? 1gb is dedicated to it but dosn't mean you can move it to the other portion.
I don't know if this is your first Android device. Maybe it's not, but you didn't notice it. I'm able to move apps to SD/usb storage within Froyo and now within Gingerbread. But this functionality does not move the whole app to SD/usb storage. For example, let's take a game I like very much, Paper Toss. If I install it in internal memory, it'll take 6,8mb of space. If I move it to USB storage, it will take 0,89mb of space in internal memory, and the rest in USB storage.
That said, you can observe now that even moving apps to USB storage, internal memory can get full. This had happened frequently in my Desire, which had only 150mb of internal memory for apps. Nexus S has 1gb, which is a great improvement, but still if I install, let's say, 300 apps (ok, that's too much, but it's just a hypothesis), I can fill all internal memory, even having some gb left in USB storage.
Just remember that I'm talking about non-rooted devices. Maybe in a rooted device with app2sd/app2sd+ one can move a whole app to sd.
If it doesn't work or causes any problems, you can undo it by going through the same steps and using "pm setInstallLocation 0"
Thanks for the tips. It works!
Here's what I did. A mix of this two tutorials:
Complete Guide to Rooting Nexus S | Mobile Phone Help and News
and
http://androidforums.com/desire-tip...apps-sd-card-unrooted-device-noobs-guide.html
Took the steps to install Google Drivers for Debug and connecting Nexus S from the first one, and the ADB commands from the last one.