Skype have pulled support for Windows Mobile, leaving only iPhone and Symbian versions of their mobile VoIP app. According to Skype's FAQ on the subject, the company "felt that Skype Lite and Skype for Windows Mobile were not offering the best possible Skype experience"; there are also hints that Skype may be planning a new version to replace it, however.
"We’ve chosen to withdraw Skype Lite and Skype for Windows Mobile because we want to offer our new customers an improved mobile experience – much like the version that has proved so popular on the iPhone, and which is now available on Symbian phones" Skype FAQ
One interpretation of their quote is that they are looking to port the iPhone version across to other platforms, potentially including the upcoming Windows Phone 7 platform set for release later in 2010. Of course, that's no good if you want to run Skype on your WinMo device now; handily there's still a hidden page where you can (for the moment) download the file.