What exactly is synced with Google? If you enable syncing to Google, what exactly is synced in a more technical way? E.g. about syncing app data, I guess there is just one standard path synchronized? Has anyone seen a more technical documentation of the synching, that describes, what exactly is synchronized?
You can check this e.g. in the Honeycomb User Guide. Basically, it sums up to the following:


Android Settings, as WiFi networks incl. passwords, user dictionary, etc.
Settings of many Google apps, as e.g. browser favorites
Apps downloaded from the Playstore


Additionally, app developers can use this API to have their apps data backup'd along -- but only few do so. Furthermore I wouldn't rely on this backup -- there are many reports that, while the backup works, the restore not always does: It seems there's no way to manually trigger it, and on initialization after e.g. a factory reset (or with a new device) it often fails. also, as far as I know, it's an all-or-nothing thing: You can have it let all your backed-up data restore (as described before), or not.