Skype 4.1 for Linux has been released yesterday. Unfortunately, there's no official changelog, but one new feature is obvious: an option to sign in with a Microsoft account and chat with your Windows Live Messenger friends from Skype.
When you start Skype 4.1 for Linux, you'll have two login options: one using your regular Skype account and another option to log in using your Microsoft (Windows Live Messenger) account.
If you choose the WLM option, you will be asked to merge your Skype and Live accounts if you haven't done this already. This is only done once and don't worry, you can still sign in using your regular Skype account if you want: simply sign out and you'll get both login options again.
Once you've logged in using your Microsoft account, you'll be able to talk to both your Windows Live Messenger and Skype friends from a single interface.
Skype 4.1 Ubuntu fixes
If you get an error when installing Skype 4.1 or you can't install it at all due to dependency issues, firstly remove any previous Skype version you may have installed:
And then try to install the downloaded Skype .deb file.
sudo apt-get remove skype skype-bin
If you're using Ubuntu 64bit and the tray / indicator icon no longer shows up, make sure sni-qt is installed for 32bit architecture:
sudo apt-get install sni-qt:i386
For other issues, including green, scrambled or black video image, see the Skype 4.1 known issues.
Thanks to bhaismachine for the tip!