Sync without gmail playing big brother?
You can easily limit what data is synced by navigating to Settings > Accounts and Sync. ( Your menu may look somewhat different than this but should be similar.) From there you can deselect Background Data, Auto-Sync as well as individual accounts such as your Google (@gmail), Facebook, etc. However, I believe this will just prevent syncing from occurring automatically. If you open the GMail application, I believe it will sync your inbox/outbox/etc. BUT, if you're not using GMail, this wouldn't apply to you.

While you're at it, you can navigate to Settings > Connect to PC > Default Connection Type. There you may have another option regarding Syncing (with a PC). I see "HTC Sync" but I'm not certain what other manufacturers have in that menu.