Jackson is a reminder that prospects are never a sure thing, especially pitchers. In 2003 at age 19 Jackson pitched well in AA and was 2-1 with a 2.45 ERA in 3 starts with the Dodgers. After that season John Sickels had him rated as the #3 pitching prospect and Prospectus had him as their #6 prospect. Since then he has struggled considerably.
Tiffany was a 2nd round pick out of high school in the 2003 draft and will turn 21 this month. He pitched fairly well in the FSL this season, though he struggled a bit with the long ball - 17 HRs in 110 innings.
The Devil Rays have considerable positional prospects but are lean on pitching prospects, and their main pitching prospects (Neimann and Townsend) have had injury problems. Prior to this trade Peter Gammons noted that the Rays have had difficulties acquiring young pitching in trades. Apparently Tampa felt that a former top prospect and a pitcher that hasn't been above high A ball, neither of who were in Baseball America's top 10 Dodger list this year, were the best that they could acquire for a reasonably priced closer and a cheap, average reliever.
(And did you know that both Baez and Carter are former All Stars?)