My understanding of the waitlist is that they dip into the pool of waitlisted applicants once the class is set, and if they're missing seats they invite from the waitlist, so I thought that you wouldn't hear back until maybe July or even August, after the last confirmation deadline.
However, during the RPSC, I spoke to several students who either got an admit from the waitlist or know of someone doing the same, but I think that these students were very proactive. Rewriting the GMAT and scoring higher, in some cases up to 50 points higher, getting new recommendation letters, etc. Basically they did whatever they could to improve their application based on what the adcom said were weaknesses.
Speaking of the RPSC, it was a fun event. Very stressful, very busy, but it was fun. Great learning experience, met tons of new people and future classmates.