Although I have never used one because birds here in Florida are not very flighty, I have seen the use of many of hides, even hydro-hides to be able to get fairly close to subjects without disturbing them.
If you do, do you rent space in one, build your own?
Here is a video of a great Spanish Bird Photographer, about hides, and what you can get from them.
Over the top bird images, behavioral videos, time lapses and just pure joy to watch if you like nature.
Enjoy!
http://vimeo.com/88058235