A source has disclosed to World of Apple that Apple is planning to hold an event on March 24 to unveil new desktop hardware. The source which has been confirmed to be in reach of such information stated that the event would be similar to the notebook event held by Apple last October.
World of Apple's source was unable to offer any details on hardware specifics but did speculate that the Mac mini, iMac and Mac Pro would all be refreshed.
[Update] My Apple Guide who has historically had a rough track record has reportedly had multiple anonymous sources suggest the same date for an Apple event.