Annotations and code pads
Annotations are stored locally and synced when you are online. Your monthly allowance and how much of it you have used are both shown in account settings; every paid plan is unlimited, the free Starter plan is capped.
Usage counted while you were offline is reconciled the next time you sign in, so the figure in your account is always the authoritative one.
Code pads
Code pads are available on every paid plan. Import one with File → Import code pad.