As far as Delic, the guy is basically a Max Mirnyi clone, as far as I can tell. No slam winner there. Donald Young is too young for anyone to predict his success, but being #2 in the jrs. as a 15-year old is pretty impressive.
Roddick will win 4-5 slams, at best, by the time his career is over- I just don't see how he is going to be able to win more than one or two until maybe the end of the decade, since Federer will dominate Wimbledon, a renewed Safin will be a major threat at the AO and US Open, and Roddick has no shot at the French.
As for Fish, he actually has a pretty good game, with pretty good groundies, a good serve, and decent volleys, but being on Brad Gilbert's "Top 5 slowest players in the top 100" (Incidentally, also on that list were Jan-Michael Gambill, Taylor Dent, J Johansson, and Ljubicic)- and having a reputation for a poor work ethic=Permanent 30-50 ranked player.
Blake is done as far as being a threat for even a deep Slam run. He has a good forehand and good movement, but nothing above-average besides that.
As for others, like Ginepri, Dent, and their ilk, they are all just average tour players.