I don't know if you are thinking about just ordering a couple of pictures, or plan on getting a CD full of them. The pictures individually can be around $15 each, so if you think you will get a bunch, the CD is a much better deal. You can put ALL the pictures on the CD and they give you a copyright release so you can print them anywhere. If your kids like to take pictures with the characters, you can get a ton of photopass pics as the majority (but not all) the characters have photographers with them. Our last trip, we had close to 200 photopass pictures, and by the time I added, autographs, borders, sizes, zooms, crops etc., we wound up with almost 900 pictures on our CD. You get a discount if you pre-order.Here is the link where you can pre-order the CD:
http://www.disneyphotopass.com/previsitcdplan.aspx
I have heard if you don't like the pictures when you get home, you can get a refund instead of getting the CD, but that has never happened to us.
Be careful about previewing in the parks. You have 30 days to input your photopass number. Once your photopass number has been input then, you only have 30 days to edit and order the pictures. If you input the numbers at the parks it will start your 30 days running, so if you do it to look at some on the 1st day, and you are staying a week, you cut a week off of the time you have to edit and add borders to the pictures at home. You can spend ALOT of time editing pictures. You can zoom and crop, create different versions with multiple borders, autographs etc. If you add borders, you also need to save the pictures in the different sizes you might want to print, otherwise, when you print some of the borders can be cut off. The photopass site has other products too. You can create books, mousepads, christmas ornaments, etc. The last 2 trips we have pre-ordered the CD/Book combo and we love our books!!!