In my last 3.0 campaign, I also eliminated the class/cross-class distinction from skills, even going so far as to have only one exclusive skill (Use Magic Device). There were *no* balance issues at all, and players did not stop playing rogues, as some have suggested would happen.
What I did find is that most (though not all) players tended to take many of the same skills early on, such as Spot, Listen, Escape Artist, and Tumble. But as the characters grew in levels, the players realized they still needed someone who was good at Diplomacy, or Bluff, or Swim, or...you get the idea. Players began to flesh out their skill choices in ways that made sense. Also, rather than one player telling another, "You have Diplomacy as a class skill - you have to take some ranks", whichever player felt the need chose the skills he/she wanted. The overall effect was more interesting characters.
The other systems suggested in this thread have many good points, but none are as simple as just eliminating the cross-class distinction. For that reason, I plan to keep using this system in the future, whether with 3.0 or 3.5 (including restricting UMD).