First off, names, the Digital IXUS 300 is this cameras European (and SE Asia) name, it is known as the PowerShot S300 Digital ELPH in the US and the IXY Digital 300 in Japan, the cameras are identical apart from the name. The Digital IXUS 300 is a progression from last years Digital IXUS, with the same 2 megapixel sensor the new Digital IXUS 300 now features a 3x zoom lens and a moderate number of improvements:

Improvements in the Digital IXUS 300 compared to Digital IXUS

  Digital IXUS 300 (S300 ELPH) Digital IXUS (S100 ELPH)
Lens 3 x optical zoom, 35 - 105 mm equiv.
(F2.7 - F4.7)
2 x optical zoom, 35 - 70 mm equiv.
(F2.8 - F4.0)
Focus range Normal: 76 cm - Infinity
Macro: 16 cm - 76 cm
Normal: 57 cm - Infinity
Macro: 10 cm - 57 cm
Resolutions 1600 x 1200
1024 x 768
640 x 480
1600 x 1200
640 x 480
JPEG modes Super-Fine
Design New designed case, new shutter release button, improved exposure dial, new power button, new zoom controller  
Volume 179 cm3 133 cm3
Weight (inc. batt) 275 g (9.7 oz) 210 g (7.4 oz)
Digital Zoom Smooth up to 2.5x Either 2x or 4x
Colour filter GRGB CYGM
Movie 160 x 120, 320 x 240, 640 x 480
(with audio)
Direct Print Yes No

Those are the specification / design differences, lets get on to examine the camera in a little more detail and see what other improvements have been made...