iOS Wi-Fi Sync 2.0 beta launches on Mac
Wi-Fi Sync works well, but the initial setup takes some work. First off, you'll need to jailbreak your phone and buy Wi-Fi Sync ($10) from the Cydia Store. Next, you'll need to install the Wi-Fi Sync desktop app (which is Mac-only) and launch it before you launch iTunes. Finally, launch Wi-Fi Sync on your iPhone and enter a code from the desktop app to pair your devices. Voila! Now you're ready to sync over Wi-Fi.
Okay, it might not "just work," but it's a decent enough placeholder until Apple finally builds wireless syncing into iTunes.