Firstly, thank you Jennifer, the instructions worked, i saw the (VERY)little blue message, let go of buttons, viola. =) it worked for me. So, that little trick wipes the cache for EVERY app, function, doo-dad & whatever, right?. . .... because I found this for the keyboard specifically:
go to Settings. ..>Application Manager ..>swipe over to ALL, select Samsung Keyboard > Clear data, cache. ...<-----i figured this out just before i tried your trick.
But i would agree that the stock keyboard is just in-general, laggy and weak. As is the stock function for "Clear Memory"; neither are as efficient as a decent free app would be for each function, would take up negligible space and oh yeah, FREE =)