CNN just did a piece on the growing trend on online digital printing.  The article notes the ease of use, low cost, quickness, the marketplace, etc.  All in all a pretty good introduction article on the topic.

We have been doing printing via Costco (which is using Snapfish as the backend) for the last couple of months.

Some of our "test" results:

• Send them the biggest pixel picture you got, if you downsize you’ll miss some clarity and color.
• If you do fancy boarders or add thier online artwork, the picture quality seems to go down.
• Using the Internet Explorer plugin on Windows makes the uploading easier.
• Turn around time is pretty fast.