The first thing one notices about the Pentax Optio S is its size. Pentax boasts on its Web site that the camera is small enough to fit into a can of Altoids.
Having lived in Hong Kong all my life, I have no idea what an Altoid is, but the point is taken, and the camera is very small for the number of functions it can perform.
At 8.3x5x2cm, the Optio S is probably on the bulky side compared with other ultra-compact cameras, notably the Casio Exilim S and M series, which are about half as thick.
But bear in mind that the Optio S packs in a 3x optical zoom, which probably makes up much of the added bulk.
In terms of picture quality, Pentax digital camera images generally tend to shift towards yellow and those from the Optio S are no exception - especially in low light conditions - although to a lesser extent than with previous models.
For more accurate colour rendering, the Olympus Stylus 300 Digital is probably a better bet, but the camera is twice as thick.
Its 3.2-megapixel capability is also at the cutting edge of what is available in ultra-compact models at present. However, watch out for the Stylus 300's sibling, which should available soon and will have a four-megapixel capability.