are there any lag fixes for Samsung Galaxy S that don't require rooting the phone? It seems like the Samsung Galaxy S is notorious for its occasional lag.  Various lag fixes are out, but most of them require me to root my phone. 

I am reluctant to void the warranty on my phone, so I would like to avoid rooting it if possible.  

Are there any lag fixes out there that don't require me to root the phone?
Yes

You can lagfix without rooting by flashing a kernel like Voodoo through Odin.

But

This will void your warranty anyways.

If it helps, the SGS phones are very easy to unroot and revert to stock to hide what you did.