Update: Apparently, according to Edios, there's to be no Thief 4 reveal at E3, as it will be concentrating solely on Deus Ex: Human Revolution for the event - per Connected Consoles.
Nothing was said about an announcement before or after that though - not saying there will be either - just throwing that bit out there is all.
Original: A new entry into the Thief series got a bit of legs today, thanks to a tweet from Sony pointing to the placeholder site for Thief 4.
Not much to go on other than the tweet, but it's out there at least.
If you look in the Twitter feed, the post has been removed, but thanks to lovely Google and its cache magic, there it is for the world to see.
Considering the game was said to have grown "leaps and bounds" back in November - it may just happen and at least the tweet gives us an indication of one of the platforms it will be released on.
Keep your fingers crossed, then.