Hi Robin,
So far I have noticed that the photos are going on the CD they way they are uploaded. I didn't have to "search" to find us on our first one. The photos were in the order of the upload. I am going to be getting CD from our 2nd group in about 2 weeks and I will take time to notice how the photos are in that cd.
Does anyone else have an answer to this question?
Thanks, April
I'll try to help.

The photos on the CD will be in the order that they show up on the online account. The order of the photos on the online account will be determined by how they're uploaded. Each photo is assigned a sequential number on the online account. A family's photos may be grouped together or they may be mixed with another family depending on when the photopass cards were added to the online account.
If someone waits until after their trip is over to add their photopass cards, then their photos will show up together in a group (for example, maybe pictures 200-400). The photos may have been taken over the course of a week or so, but the expiration date of the photos on the online account will all show the date they were uploaded.
If someone adds their photopass card while they're at WDW (say they have a laptop with them), then their photos will be uploaded gradually each day when Disney quality control releases the photos. If another family is also at WDW at the same time and has added their photopass cards, then these 2 family's photos will be mixed together. The expiration date of the photos will be the date they were uploaded, which will be varied dates throughout their trip. We uploaded while we were at WDW, and we noticed that some would show up online the night they were taken, and some would be delayed until the following day.
One very good thing is that when you make an edit to a photo to add a border or icon, it creates a copy and give it a sequence number just after the original photo. So, if you edit photo 100, then it will be saved as photo 101. This makes it relatively easy to tell if you've already made an edit to a photo.
In my experience, I'd estimate that someone on an average week long trip will end up with between 300 & 500 photos (included the edited ones). Obviously, some will have more and some will have less. Each photo is 2 meg, and Disney puts 300 photos on a CD. Based on this, I'd estimate the large group with 13 families may have about 5500 photos on their online account! I had a group with 5 families, and we ended up with 1900 photos. I can tell you that the photos at the end (mine) took a while to get through on the online account to display them and work with them. 5500 photos could be a total storage of 11000 meg (or 11 gig, right?). Disney would be sending 19 CD's for this many photos. How much fits on a DVD? I looked at some we have, and it looks like 4.7 gig, so I guess this would take 3 DVD's to fit them all. That doesn't sound as bad as I thought it might be.
Let me know if there's any more questions. I was able to identify the pics from the different families in my group even though 3 families were intermingled, and each family only received a small number of photos that weren't theirs. But I only had 5 families, and they were relatively easy to identify...
Good luck with everything!