As I look around the forums about typing lag issues, it appears that the most often used remedy is a factory data reset.
I'd first have a look at resource draining apps/widgets/services and see if there may be some settings that can be changed, perhaps manually syncing some of them instead of autosync (especially weather and news widgets, along with Gmail).
In addition, some users discover an app or widget that is not playing nice with the system.. it could be anything, but most often turns out to be a task killer or other app that is supposed to monitor things; they'll remove that and things go back to normal following a reboot.