Test three: Ease of use
This category is harder to judge because these programs all have flaws.
iPhoto is the simplest, but little things can still trip you up (where exactly has it put your photos?). And despite being revised in the latest version, its geotagging/mapping tools are still hard to fathom.
Picasa's problem is that it's a cross-platform app that uses an effective but odd folder display and management system quite unlike what Mac users will be accustomed to.
Photoshop is, as you'd expect, very technical from the start, and while Elements is a lot better, it tries a bit too hard to help you - sheer choice becomes confusing.
Aperture and Lightroom are professional apps, so you're dropped in at the deep end. But it doesn't take too long to figure out the basics. Aperture is the one with the most longterm flexibility, but you'll figure out Lightroom quickest, since it's not too big a step up from a file browser like Adobe Bridge, and the tools are less daunting.
Test four: Value for money
Picasa looks like it's the best value for money since it's free, but then you could say the same for iPhoto, which is paid-for only if you upgrade from an older version.
At the opposite end of the scale you've got the hugely expensive Photoshop, which doesn't do a whole lot more than Elements, at least as far as photography is concerned. In fact, given that the Organizer app supplied with Elements is actually more effective at organising photos than Adobe Bridge, Elements looks better still.
But let's not rule out Aperture and Lightroom. Neither is cheap, but both are highly capable apps designed for pro photographers. Of the two, though, Aperture is the best value because it's significantly cheaper.
In the end, though, we'll go for Elements. iPhoto and Picasa might cost nothing, but they lack depth and and you could soon outgrow them. Photoshop, Aperture and Lightroom deliver diminishing returns for amateur snappers.
The winner: Photoshop Elements 9
We were looking for the application that delivered the best all-round combination of photo organising and editing tools, ease of use and value for money, and the program that ticks all the boxes is Photoshop Elements 9.
It offers a large proportion of Photoshop's image-editing tools at a fraction of the price, and the new Organiser app is powerful and simple. Its one disadvantage is its old-school approach-switching between two separate apps for the editing and organising functions.
If this gets your goat, look at iPhoto and Picasa. They cater well for the beginner, but don't offer enough for enthusiasts, while Aperture and Lightroom cater very effectively for professional needs.