Thus far, I have uploaded rarely (2 images so far), but I expect to be more prolific as I become satisfied with the medium and what I produce with it. That being said, it costs money to maintain data and serve it up. If you have a lot of data, it can cost a lot of money. I think it is fair to limit either the total number of images, or the size of the files uploaded. Limiting the file size is probably the best solution.