Will have to wait and see what happens at the WWDC. That is set to reveal the future of iOS and OS X.
I would be surprised at the moment if we see the 5 that early. Especially as a lot of components are made in Japan. Most of the usual reliable sources suggest around Sep and some pushing the boat out till Xmas.
We may see an upgraded 4 (a bit like a 4GS) which has the A5 chip in and an increase in capacity.
I do actually know but my uncle steve has sworn me to secrecy. All i will say is that i am posting this from an iDevice and i am not physically touching anything nor am i speaking.
Another clue is the film Firefox