Like most other things you hear about Diablo 3 and Starcraft 2, this is purely a rumor until it comes directly from Blizzard. It was grabbed from a Korean site thisisgame.com.
"Starcraft 2 will be announced to the public on May 19th at the Blizzard Worldwide Invitation (WWI).
On April 25th, according to the game company Blizzard Korea Entertainment, it is confirmed that they will announce Starcraft 2 demonstrating it with both videos and images. Furthermore, the developers of Starcraft 2 will be there, and have time to answer the questions.
Starcraft 2 is being developed in 3D and there will be new race and some specific changes to remaining races. Details of only minor parts will be released at WWI.
Blizzard invited more than a hundred of broadcasting teams from around the world for this announcement. Prior to this very secret moment on May 19th, they will not release any information.
However, from the people who previously worked with Blizzard, there is trusted word about this information. A person who recently retired from Blizzard said there is development of Starcraft 2 and there will be an announcement.
The chairman of Blizzard Korea said “we cannot answer anything about Starcraft 2, we will have a new game on 19th so please come and find out”. He refused to answer if new game is Starcraft 2.
The shout caster “Um Jae Kyung” said “I expect it to be very balanced but have concerns regarding E-Sports, but I doubt there will be changes about E-sports in regards to Starcraft I. However, there will be most likely be another league for Starcraft II and e-sports will be much bigger. Since I’m one of the gamers, I’m very excited about this”.
The 3rd WWI will be on May 19th ~ 20th in Seoul, and it seems there will be a lot taking place."
Blizzard has stated!
"We do intend to announce a new product at the Worldwide Invitational next month in Korea, and we appreciate the enthusiasm and interest in getting an advance look at what that will be, but players will have to wait until May 19th to find out more. Also, we have a very strong connection with the characters and settings of StarCraft, and we do plan to revisit that universe at some point in the future, but we don't have anything new to announce in that regard at present."
So May 19th we will finally find out what blizzard has been working on, Starcraft 2, Diablo 3, or something totally new.
:cry: 
ps. sorry i posted it in tabletop games but this seemed the most accuarte forum to post to