Interesting trade. At this stage it's pretty even, although SD could end up running away with it.
Webb is a rare reliever who gets mega-GBs (62% in 2010). If he can lift his K/9 rate from 6.7 into the 8 region he will be teh sex for Florida for a long time. Florida have an unusual bullpen now, with 3 set-up/closer-y pitchers who generated 50%+ GBs in 2010 (Hensley, Nunez, Webb).
Maybin has really got to bridge the gap between his decent minor league and his atrocious majors BB/K, otherwise he'll be a bust. Luckily he's only 23, so he's got some time.