I agree that a simple thank you should be the minimum requirement. Even tho it is wonderful to see a photo of the contents, not everyone has the skills to take or post photos.
To help Lori, perhaps we, the senders, could also send a PM to say we have had a thank you. I have posted a thank you on thread and forgotten to PM Suzanne for a week or two.
It was not until Suzanne posted a list showing who had received a swap that I realized that I had not PM'd her, so I guess this is helpful. If someone is a persistant offender of not saying thank you, say after 2 months, they should receive a reminder of the rules. Then if they still transgress perhaps they should be excluded.
We should be mindful, as it has been pointed out, that life does sometimes gets in the way. I always intend that the next swap will be mailed early, but always my life gets tangled up and I am either on the deadline or just over it. Being 'International' this means that my parcel takes a long time to arrive. However a lot of time, love and effort still goes into it.