I did the on-line check in, they sent me an email and a link.... But I believe you can just log on to the WDW site and do it that way.... takes 5 min and is way easy!!!
I checked in yesterday for our Sept. 18th arrival. The trip was booked through Dreams Unlimited and I didn't have any trouble. Let's hope when we get there it will be quick and easy.
If you do it online correctly you will receive an email confirming your reservation and checkin! Ours was easy and no problem with it - we got the email in about 15 minutes later!