Which specific storage space is low, when getting "Low Space" on Samsung Galaxy S?
It is usually /datadata that gets full on the Galaxy S. Interestingly this partition is not displayed in the Storage Setting Menu. The quirk is that /datadata is mounted on a special very fast flash chip that only provides 170MiB of storage space.

While this was enough in the "early days" of Android when the Galaxy S was released, it can easly become tight with modern Apps. /datadata is used to store application user data, and while many apps only place a few KiB there, some apps require to store more. Typical candidates that store around 20MiB in /datadata are Google Chrome and Google Currents.

ATM the best practice is a fix that lets you control which apps can store data on the fast chip and which are outsourced to the slower RAM. This script can also be installed with an app called datafix.

To find the apps that consume the most space use su &amp;&amp; du -s /datadata/* |sort -gr |head. For example on my device:

shell@android:/datadata # su &amp;&amp; du -s /datadata/* |sort -gr |head                    
39180   /datadata/com.android.chrome
20809   /datadata/com.google.android.apps.currents
16763   /datadata/com.google.earth
9431    /datadata/com.google.android.apps.plus
8938    /datadata/com.inisoft.mediaplayer.a
8270    /datadata/com.google.android.apps.maps
3015    /datadata/com.google.android.apps.docs
2160    /datadata/udk.android.reader
2096    /datadata/com.android.providers.contacts
1597    /datadata/com.fsck.k9