Unending Description

Marci Baun suggested this month's topic: What is the description saturation point for a reader?
I have to admit, as much as I love good, emotive description, my description toleration is relatively short. I know unending description quickly becomes boring for me. What is its purpose? How does it further the story? What is the author trying to show me?
Once someone who knew I wrote told me she wanted to write, too, but she always got stuck on the plot line. She said she loved description, and raised a hand to a nearby window and became involved in telling me about the view, telling me that was what she wanted to share with readers. Her hand moved with the description of what she saw in a moving tableau of where she wanted to take a reader. She wanted the reader to see everything she saw and sensed, how the light affected the atmosphere and how it illuminated all the objects both living and nonliving; how the shadows could be mysterious, and all the details of everything she imagined. She was stuck on description, not plot.
Description is necessary in writing as the detail provides a sense of place and character, but I feel that any writing technique draws attention to itself, it draws the reader out of the story. When that happens, the reader often quits reading.
Good description attracts the reader in a sensual way since most description relates to taste, feeling, scent, sound, and vision, and provide keys that invoke the reader's memory. These experience reflections engage the reader unobtrusively in the story. If a scent is mentioned and the reader has encountered that smell in reality, their memory recreates a mental judgement whether it was a good or bad experience, bonding them to the story.
For me, description often works best when the author inserts a few carefully chosen descriptors into a sentence whose intent is other than providing description; a kind of fly-by that doesn’t stop the story but viscerally adds to it.
As with all writing techniques there are exceptions. Long descriptive passages are occasionally necessary because a setting is so sumptuous, so extremely offensive, or so strange, it needs an extended description. I believe one key to delivering this type of exception is to keep the character moving through the scene, giving detail as they encounter what needs describing, mixing character, action, and description.
Like many writing techniques, description is a balancing act between too little and too much. Too little leaves the reader unmoved, too much overwhelms. Description is necessary, but can make or break the story. 

Check out the following authors and their comments on description:

Marci Baun 
Skye Taylor
Beverley Bateman
Anne Stenhouse 
Dr. Bob Rich
A.J. Maguire 
Rachael Kosinski
Diane Bator