The 16-megapixel PowerShot SX500 IS was a good camera for what it was: a reasonably priced, very small and lightweight ultrawide-angle 30x-zoom camera that offered more shooting options -- including semimanual and manual controls -- than most in its class, with very good optical image stabilization.t
Judging by the specs, the new PowerShot SX400 IS is basically the same as the SX500 IS, but without the semimanual and manual shooting modes and with a lower-resolution 3-inch LCD.
It does have an updated image processor, though, which could potentially improve picture and video quality. At the very least it seems to have enabled Canon to add its ZoomPlus feature, which digitally doubles the 720mm maximum focal length to 1,440mm.
Look for it in August in the US for $250 (converted, about AU$270 -- see Canon's site for more) and in the UK in September for £259.