Songbird 1.8 beta 3 was recently released, and even though it doesn't offer Linux support anymore, it still runs on Linux and since Nightingale (a Songbird port which is supposed to bring support and enhancements to Linux) advances very slowly (in fact no version was released so far), if you're a Songbird fan you might as well give the latest official beta version a try.
Running Songbird 1.8 beta 3 in Ubuntu is fairly easy (I'm not sure if this will work with any Linux distribution, that's why I say "Ubuntu" - because I tested it in Ubuntu): just download it and remove all the gst*.so files or else Songbird will fail to start.
The easiest way to run Songbird 1.8 beta 3 in Ubuntu is to copy/paste the following commands in a terminal (it will download and run Songbird for you):
cd wget http://download.songbirdnest.com/installer/linux/i686/Songbird_1.8.0b3-1747_linux-i686.tar.gz tar -xvf Songbird_1.8.0b3-1747_linux-i686.tar.gz cd Songbird/ rm lib/libgst*.so ./songbird
cd wget http://download.songbirdnest.com/installer/linux/x86_64/Songbird_1.8.0b3-1747_linux-x86_64.tar.gz tar -xvf Songbird_1.8.0b3-1747_linux-x86_64.tar.gz cd Songbird/ rm lib/libgst*.so ./songbird
Also, from now on you can start Songbird by going to the "Songbird" folder in your home directory and double clicking the "songbird" file (attention: not songbird.bin!).
Thanks to LinuX Freedom for Live for the tip!