No. I think 1.1/devel is as stable as 1.0. I use it for all my projects.
Note that there are quite a few significant changes for 1.1, so if you migrate, you have to change some code to get your application working again.
Can i find the list of deprecated or removed functions in github or somewhere . i have figured out some deprecated functions like factory() to forge() and changes in array classes i think i can handle the change. so thank u for the response WW
Mmmmmmm ... you can try to change and take a look to the log file ( when you can see the messages about deprecated functions
In 1.1 dev there are some functions ( like Html::br(), ... ) that have been removed ( not deprecated ), so you have to refactor your code
1.1 is pretty stable but big changes might happen and from time to time there might be a bit of not-fully tested or unfinished code in there. It always has the latest bugfixes, but it's also where changes happen. For production sites I'd suggest you use the latest stable release, for development I'd recommend 1.1-dev.
For the changelog: https://github.com/fuel/core/wiki/Changelog-v1.1 - not complete but all big changes should be in there.