The Collaborative International Dictionary of English v.0.48:

Swimmingly \Swim"ming*ly\, adv.
   In an easy, gliding manner, as if swimming; smoothly;
   successfully; prosperously.
   [1913 Webster]

WordNet (r) 3.0 (2006):

swimmingly
    adv 1: with no problems or difficulties; "put the plans into
           effect quickly and smoothly"; "despite of some mishaps,
           everything went swimmingly" [syn: smoothly,
           swimmingly]

Moby Thesaurus II by Grady Ward, 1.0:

27 Moby Thesaurus words for "swimmingly":
   beyond all expectation, boomingly, easily, effortlessly, facilely,
   favorably, flourishingly, fortunately, handily, hands down,
   happily, lightly, like clockwork, like nothing, no sweat,
   on easy terms, prosperously, readily, satisfyingly, simply,
   smoothly, successfully, thrivingly, to good purpose,
   to some purpose, well, without difficulty