In a series of tweets today, CNET's Brian Tong claims that Apple's iMac will receive an update that will debut in late April or early May. According to Tong the update will take the predictable course of gaining Intel's "Sandy Bridge" platform as well as Thunderbolt connectivity.
The iMac is not expected to change in physical appearance in anyway.
My sources say New iMacs will feature Sandy Bridge and Thunderbolt. No other specifics.
The iMac was last updated in late-July 2010.