For those who want to upgrade from Nexus Ultimate (GOTD or otherwise) to Xtreme:
1. In the top right corner of the About tab of Nexus Ultimate Preferences you should see a 'Upgrade to Xtreme' button. That will take you to the 'Upgrade Nexus Ultimate to Xtreme' order page.
2. Once you've placed your order (your license key will be sent soon after that), here is what you should do:
a) Open the Advanced tab of Nexus Ultimate Preferences and Backup your Nexus Ultimate settings to the DESKTOP folder (do NOT store the settings file to the normal backup location as that will be removed on uninstall).
Now you have two options: you can uninstall Nexus Ultimate or install Winstep Xtreme on top. If you chose to uninstall Nexus Ultimate, it's probably a good idea to tell the uninstaller that you want to keep your settings and themes (otherwise you'll lose any themes you have downloaded since installing Nexus Ultimate). If you decide to install Xtreme on top, the 'Winstep Xtreme' entry will replace the 'Nexus Ultimate' entry in Add/Remove Programs , but, after installation you will have to manually delete the 'nexus-ultimate.exe' file from 'C:\Program Files\Winstep\' (or 'C:\Program Files (x86)\Winstep\' if you are running a x64 bit version of Windows).
c) Download and install the trial version of Winstep Xtreme v10.6 from the Winstep web site.
d) Open WorkShelf Preferences and Restore the previously saved Nexus Ultimate settings.
e) Once you receive your license key, follow the instructions on the email to register your copy of Winstep Xtreme (the trial is 100% functional and all the key does is allow you to use it past the 30 day trial period). Please note that, unlike the serial number used in the GOTD version of Nexus Ultimate, the Xtreme license key is NOT something you type in, the key is self-installable instead. Just follow the instructions on the email and you'll be fine. 
Once you are fully registered, and if you would like to try the v10.8 beta which is packed with new features (see the preview video below), head on to the Winstep forums, sign up, and apply for access to the Beta Discussion forums.
Preview video of the next release of the Winstep Nexus dock: system tray on the dock, Windows 7 "superbar" abilities (even on XP) with Aeropeek (Vista/7), nine new cool dock mouseover effects, and MUCH MORE!
Winstep web site: http://www.winstep.net