Originally Posted by Shaun
Typing lag can also be from a poorly coded onKeyRelease() function of the site, or a browser add-on that is not compatible with the Rich Text Editor plug-in being used (most often a spell check plug-in).
As was posted above, check the processes first. Then try running the same page in a different browser on the same machine.
If you are using IE under Properties, Advanced, click restore defaults but be sure to uncheck "Reuse windows when launching shortcuts".