When I began my teaching career observations occurred three times a semester and they were always unannounced. I taught in a dangerous school and we had to keep our doors locked (you never knew what a hall walker would decide to toss in a room) so, when we heard the turning of the key in the back door, we knew something was up.
I remember hating those observations, but, in retrospect, they were really the best. My AP saw what I did on regular basis, not some random show I was putting on for her benefit. And, while there were certain things she looked for and expected, I knew what these were and did my best to do them in every lesson. Oh, Danielson hadn't written her framework and for all I know, she might not have even been born then, but this AP and her observations taught us all to be good teachers. Even with the lowest level students, she insisted on mathematically precise language (my former AP said he wasn't impressed with "fancy" words and wanted us to use baby words the kids could understand.) She taught discipline and she helped with curriculum. She knew who was good at their job and who was not and didn't need standardized tests to form her opinion.
The best part of the unannounced observations was no sleepless night or extra long preparation the night before. They weren't so bad at all. And, unlike the observations of today, these were designed to help, not hurt. The comments in the 3 - 5 page report were insightful and led to better teaching. A special ed AP recently told her department that the new evaluations would help her get rid of teachers she did not like. Since she is incompetent herself, she wouldn't know a good teacher if she observed one and if she did, she would not want him around and now she would could be as clueless as ever and just follow a meaningless rubic. It is back door to the rescue of the AP.
(Picture from The Art Of The Brick--a Lego exhibit at Discovery times Square by Nathan Sawaya--amazing what this guy can do with Legos. It is a good thing Danielson wasn't around when he went to school or his creativity might have been stifled.)