Today I made my first manned trip to Gilly and back (single Kerbal getting down with jetpack to plant a flag from orbit). That was first interplanetary test of my new lifter, real test will be tomorrow when I try to land on Duna and get back (to orbit at least for refueling). Old desing could send just small probes and landers around (from Moho to Jool) So to answer question, Id say interplanetary travel and soon also returning.