You should look at all the apps you have installed on your phone. Many games or 3rd party predictive text keyboards (which access your facebook, gmail, and twitter accounts) are pulling data as you use them and remain as open tasks on your phone's system (only to keep portions of your data access and device resources tied up). If you've opened a few third party apps and exited them you may have several processes still open and eating up the phone's resources and slowing down transfer of data.
on the Galaxy S 3 you can open your task manager by pressing and holding the home button, it opens with a list of applications still running. You can close all open apps by pressing the trashcan icon.
if you select the pie chart icon, you will see the portion of available system memory (RAM) that is presently being used. You can clear this by selecting "Clear Memory".
These are things you will have to do routinely to maintain availability of your phones resources so that it runs at a reasonable speed.
Also, keep in mind that simple apps like third party keyboards can be sucking the phone's system resources with features that access your facebook, gmail, and twitter accounts to gather word usage patterns to feed into a predictive text that is tailored to you.
and there is a routine check for app updates that runs, so if you keep a larger number of apps installed on your phone, the more data required to transfer in this update check.
Very soon, we will be seeing Samsung release the first quad core processor system, and I am sure there will be greater advances in phone processing power, until then, we have to manage the system resource utilization to keep it running efficiently.
