Quote from "pollution free" (we know who they are) newsgroup:
"There are only a few software packages that can actually hold, modify and check curvature continuity (easily). These include ICEM SURF (industry standard) Alias, Imageware/Freeform, PDGS and the CATIA 5 add on ACA module. (there may be more)
Standard CAD packages like I-DEAS, UG, CATIA, PRO-E, SOLIDWORKS and RHINO cannot do this. Before people start to object to my last statement, Every CAD system can model a car body, just not to curvature continous industry tolerances. These are defined in the program, and are not as subjective as everybody seems to think."