The Casio EX-Z750 remains one of the most highly specified 7MP cameras on the market today, and it's certainly the most sophisticated of the 'ultra compact' models (it's a lot, lot smaller than the PowerShot A620). As you can see from these side-by-side shots there's not a significant difference in the amount of detail captured, although the Z750 does have a slightly higher measurable resolution. The main differences are again in the processing - the Z750's over-saturated and over-sharpened results have been well-documented, and the default saturation has apparently been reduced in the latest firmware version (these shots were taken with the original firmware), but once again which you prefer will come down to personal taste - you've got 7 million pixels to play with, so unless you are regularly printing posters the minor differences in detail and sharpness simply won't be visible. That said, as I've said before I prefer a slightly soft image that I can sharpen myself than an over-processed picture that leaves me little room for manouevre once I've loaded it into Photoshop, so my preference would be for the A620 shot.
<and at ISO 400>
At ISO 400 the difference between Canon's fairly subtle and Casio's sledgehammer approach to noise reduction has widened the gap significantly. There's more detail in the A620 image, yet despite the Z750's heavier noise reduction it still looks noisy - with nasty blotches in all areas of solid color. Few small sensor compacts perform that well at ISO 400, but the A620 is amongst the better.
Note: as mentioned previously, the Casio shots were taken with the original firmware, we are assured that the default saturation is lower if you use the latest firmware, so the results won't look quite so over-blown, color-wise.
Overall conclusion
The PowerShot A95 was one of the most successful 5MP compacts due to its compelling combination of features, image quality and value for money. But it was not a camera without problems - mainly performance and speed issues, most of which we - and all the people who bought it - put down to the inevitable compromise involved in getting so many features at such a keen price. The PowerShot A620, though externally pretty similar, is a very different kettle of fish. Not only does it boast a much better sensor, but the use of the latest DIGIC II processor means it's a lot, lot faster in operation too. There is very little here to suggest a 'budget' model at all; image quality is excellent, it's very well built, it handles well and it has a real wealth of photographic features that make it suitable for everyone from the absolute beginner to the more experienced photographer wanting lots of control over the picture taking process. And like the A95 it's a great first camera for anyone wanting to learn the craft of photography, being both affordable and well-specified enough to grow with you as your knowledge and experience increases.
Of course it's not perfect; there are some exposure issues (though these are fairly rare), it's fairly chunky and hardly lightweight, and there's still no way to change ISO or white balance without using the FUNC menu (even the most basic Ixus model now has an ISO button). But what it lacks in sex-appeal it more than makes up for in sheer value for money. Like the A95 before it, the A620 is one of those rare cameras that takes virtually every shooting situation you throw at it in its stride, with only the highlight clipping issue preventing an almost perfect hit rate.