How can I control the frequency of synchronization with Google? My phone syncs with Google pretty often.  Each time it takes a few minutes and makes the whole phone work slowly.

Is there any way to make the synchronization less frequent?

Barring that, is there any way to make it pause when I actually want to use the phone?  Is there any way to lower the priority of the sync tasks?

I'm using a Samsung Galaxy S with Froyo.
I don't know of any way to set the sync frequency or to make syncing low-priority, unfortunately.  You could use Locale to turn off/on auto-sync based on profiles you set up, however.  There's a Locale plugin that might do most of the work for you: https://market.android.com/details?id=net.andvari.android.syncsetting