i was at the Apple store at ABQ Uptown yesterday getting mine and my wifes 3g's replaced due to cracks in the back below the earphone jack and asked the "genius" about the lagging text issue/crashing apps
One thing he told me was lagging text is usually due to to many apps running in the background. if your using an app instead of just hitting the home button. Hold it down till the app closes and that should prevent lagging text.
I guess we will see im gonna try that
well that was a load of crap my new 3g replaced yesterday is already lagging during texting