I have the exact same problem. Tried everything short of a hard reset to no avail.
I don't know if anyone tried this, but the following steps produced the same problem too, even though it shouldn't:
1) Turn on both "Background data" and "Auto-sync" in "Settings" -> "Accounts & sync".
2) Tap on Google account.
3) Uncheck everything.
4) Tap the "Menu" soft-key. If the option shown is "Cancel sync," tap that. Otherwise, leave that alone.
4) Go back to the sync settings and uncheck "Auto-sync"
5) Tap on Google account again.
6) Tap the "Menu" soft-key. The option "Sync now" should be showing. Tap that.
7) Note how the sync icon shows up in the notification bar and stays on indefinitely even though nothing was selected to be synced from step 3.
8) Tap the "Menu" soft key and "Cancel sync".
9) Now individually tap the different sync options (i.e. tap "Sync Contacts," read the error message, then tap "Sync Calendar," etc.). The error message indicates you can't even manually sync those items without them checked when "Auto-sync" was enabled.
This brings up the question of "what is the phone doing when the "Sync now" option was pressed if nothing was selected to be synced from step 3 and when it won't even allow you to manually sync without changing the setup?
So, to conclude, even when all items for the Google account were unchecked (for auto-sync on
OR off), the phone still gets stuck in the syncing mode.
In the meantime, I'm keeping auto-sync off, which is like having its knee caps blown off for me
