There are a couple of reasons for everyone, regardless of your politics, to be concerned by this decision.
First, the Court definitively ok'd the partisan political gerrymander. Although it's been a part of American political life for nearly 200 years, gerrymandering has always been considered at least slightly unsavory, and redistricting for the naked purpose of shutting your opponents out of potential representation, as happened in Texas in 2002, was made to appear rare.
Not any more. Today's decision completely legitimizes this practice.
The second issue is, i think, even more troubling. And that is the separation of the decennial census from the redistricting process. What Tom DeLay attempted to do in Texas, for pretty much the first time in US history, was to get his cronies in the Texas legislature, with their newfound Republican majority, to redraw the Congressional districts after they had already been redrawn following the 2000 census. The sole purpose of this redistricting was the concentration of political power.
That this was upheld by the SCOTUS should signify a major shift in the nature of the political game.
You can expect that the states in which Republicans hold legislative majorities will soon be engaging in their own redistricting before the 2008 elections, in order to change the Congressional map. Democrats who hold majorities in state legislatures who do not realize this and act accordingly are signing their own death warrants.