Most obviously, Spaces are just fancy names for virtual desktops; something that can be easily achieved by VirtueDesktops, DesktopManager, and VirtualDesktop Pro. The new application launching features of Spotlight take aim at popular applications such as LaunchBar, Butler, and my personal favorite of OS X applications, Quicksilver. With iChat, tabs kill off Chax, live presentations kill off ShowMacster, and backgrounds kill of ChatFX.
Be sure to click through to the original post for all the other apps now lining up at the unemployment window, and to see what the shareware developers themselves have to say about the announcements.
Update: Buddy'o'mine and BarCamp mastermind Chris Messina has a similar post.