The picture becomes clearer each hour.
Each hour, certain numbers in the time turn green. If you take these numbers, put them in a row, translate them to letters (only 0-25 become green), and write them backwards, they turn into stuff said in starcraft (stuff from the 'ghost' unit so far, like "somebody call for an exterminator", and "call the shot").
Man, Blizzard guys must be having a blast causing all this ruckus. There is even people decompiling the sourcecode of the applet. The picture, apparently, is full of random numbers with no pattern, so its impossible to find the finished picture (though people are speculating that it'll be a zerg-protoss hybrid, or the zerg queen, kerrigan). The source also changes every hour, so decompiling has been determined to be useless.
Sounds like they've thought of everything. I'm getting excited about a game I probably won't have the firepower to play... hehehe...
I don't have links readily available, atm, but a search on google won't disappoint if you need them.