Eclipse3 - Jar Export Wizard, no Main Class

the export wizard to generate executable jarfiles seems not to be very mature in Eclipse3. there are several timeconsuming problems:

1. no class is presented in the dialog to select the main class. i checked all settings, but found no solution. a possible cause is maybe when package directories have been created using "new Folder" instead of "new package". finally i set up the complete project definition in a new project in the workspace and moved all resourcefiles.
2. compile errors during the the jarfile generation are reported, but the cause is not reported. in my case, no errors are reported in the projectworkspace (even after complete rebuilds) but jargeneration signals some compile errors.

Maybe it is better to build the jarfile by hand using jar -cvf etc.