The only way to describe using the Ubuntu OS and the daily pleasant surprises I get is to compare it to Christmas coming everyday. Honestly its no exaggeration. In my view no OS is better, Ubuntu is just BOSS, period!!! ... and it keeps getting better.
The latest 'Christmas present' comes in the shape of fb4linux a port of the Adobe FlashBuilder for the 'nix' platform. I give my heartfelt THANKS to the wonderful person who has spearheaded this project. Once set up its a perfect working copy of FlashBuilder. I really was not keen on the idea of installing Wine in order to experiece FlashBuilder, and though I could install in VirtualBox that would mean I'd be developing in Windows which I did not want to do.  There is the usual problem of there not being a designview in this IDE as well but, I've been developing on FlexBuilder for Linux for so long that frankly I do not miss it at all.
I installed fb4linux on Ubuntu Karmic 64-bit, my Eclipse build was Gallileo. By Golly does it rocket when you compile, you hit F11 and before you can say 'F11' your build is up. There are some set up procedures to adhere to if you are developing on a 64 bit linux distro. You need to set up a 32 bit Eclipse build as neither FlexBuilder nor FlashBuilder can be run on the 64 bit versions of Eclipse. The instructions for doing this are detailed quite clearly  on this blog .
I have copied the main parts of the blog post relevant to setting up FlashBuilder here (this was how I set it up) on the assumption that you have downloaded Eclipse Gallileo and the fb4linux project zip. With a Ubuntu Karmic 64 bit you need to install ia32-sun-java6-bin and all its dependencies.

1. For 64 bit: In a terminal window run “sudo update-alternatives –config java” and select ia32-java-6-sun as your jre of choice.
2. Unpack your Eclipse download and place it where you want it to be, I like /usr/local/bin/eclipse-galileo, by running “tar zxf eclipse-SDK-3.5RC2-linux-gtk.tar.gz” to unpack it.
3. For 64 bit: Move the eclipse.sh script into your eclipse install folder and run “chmod a+x eclipse.sh“.
4. For 64 bit: Set java back to the regular 64 bit variety using the same method as step 1 (but obviously selecting just java-6-sun).
5. Untar the fb4linux package in a folder of your choice. I would suggest you have a parent directory called FB4Linux and untar your package in here. Mine was placed here home/ayo/Adobe Flash Builder Beta 2 Linux
6. Download the Flash Player 10 debug player for Linux from Adobe. Create a directory wherever you like and place the standalone player there. Mine was placed here '/home/ayo/DebugFlash/
   

Please restart Eclipse after you have done this to be certain that Eclipse works. Once you are in Eclipse go to Help>Software Updates> Configuration. Add the path to where you untarred your download of fb4linux. Thats it - done. Well almost. You need to create an 'sdks' folder in the parent folder, in my case the 'Adobe Flash Builder Beta 2 Linux' directory. You need to set up your SDKs and the location of your web browser and standalone player, in my case /home/ayo/DebugFlash/flashplayer.
Now create your first test project and enjoy the goodless of Ubuntu and FlashBuilder

For a very LIMITED time only download FB4Linux here