I think I have just made a nasty discovery. Arduino IDE saves sketchbook files in the Windows/Temp directory not in 'My Documents' as I believed (It says so at the bottom of a sketch doesn't it? 
) After a clear-out I found I lost much of the sketch I am currently working on!! Of all the damn fool places to save important files! Is there any way of choosing a different location for sketch-book files?
The reason for the clear-out was that I have been trying to install Atmel Studio 6 but unsuccessfully. I have repeated my attempts so many times (latterly under the guidance of Atmel) that the Temp file directory was stuffed with Atmel installation files. The Arduino files got deleted at the same time!
Has anyone else had problems with Atmel Studio 6?
In the IDE, open File:Prefences, and set a Path, your sketches will get saved there.
For example, I use C:/Users/Documents/my_user_name_on_my_laptop/ArduinoStuff
or something similar that fits the Win7 environment.
I gave up in using Atmel Studio because it took forever to start up under WinVista on an older laptop.
I have not tried it on my newer Lenovo W530 with i7 processor and more RAM & stuff.
Adrifran39:
I think I have just made a nasty discovery. Arduino IDE saves sketchbook files in the Windows/Temp directory not in 'My Documents' as I believed (It says so at the bottom of a sketch doesn't it? )
On my Mac it stores sketches (and local /libraries and /hardware) in:
Macintosh HD/Users/john/Documents/Arduino
It puts the build results in a temporary folder but since it re-builds from source every time you upload a sketch you don't need to save any of the build results.
Did you accidentally set your "Sketchbook location:" in Preferences?
Thanks John and CrossRoads. I didn't change anything ---- I think ----but my project, a Greenhouse controller, which I have been building for some time opened in a state I had saved a couple of weeks ago! The lost data was not obviously discoverable so I blamed the last thing I had done, which usually is correct.
Sometimes the IDE doesn't seem to save when prompted. I always save a backup but I can't seem to do a 'save as' and change the filename to the backup filename - it just won't have it.
The backup file when opened had not lost as much work as the current file but it had lost some.
It is possible that in my dotage I forgot to save but both files?
Ho hum, one of life's little reverses!
As for Atmel Studio 6, I carried out all of Atmel's latest directions - an afternoon of un-installing and re-installing all to get the same failure!