Aperture is not for everyone but it has always been a competent way to organise and process large numbers of photographs and images. For people used to iPhoto, this application could always seem large and daunting and not always intuitive. But to the experienced amateur and professional photographer it has provided a very good way to handle the large number of images generated in a typical shoot. Adobe's Lightroom has been a very successful competitor and has the advantage (from a sales volume point of view) that it is available on both the Windows and the OS X platform. Aperture is strictly for the OS X platform. Aperture 3 upgrades this professional level package to add some of the nicer features of iPhoto and thus make this package more appealing to the amateur photographer that produces lots of photographs and needs something a little more powerful than iPhoto. The major advantage of Aperture has always been that editing is non destructive as opposed to iPhoto which makes a copy thus increasing your library size each time you make an edit. Thus libraries can be become very large in iPhoto when edits are made in large number of photographs. Also Aperture's ability to apply corrections to batches of photographs as they are imported and the powerful search tools make organising large libraries much easier than with iPhoto. However Aperture 3 adds events and a powerful slide show editor making it unnecessary to use iMovie and iPhoto to produce professional slideshows. Aperture's biggest advantage over Lightroom remains the fact that it will also organise those short video shots produced by a lot of still cameras (usually P & S but now increasingly DSLRs). These can be incorporated in you slide shows and makes for a very convenient all in one package.
All in all Aperture 3 is a worthy update to Aperture and allows the enthusiastic amateur to use this package instead of having to use iPhoto and iMovie to make those slide shows for the family and friends of that party etc. The only disadvantage of moving Aperture into the one and only photo organiser and processing role is that integration with other Apple applications is buggy. e.g. If you sync photographs with Apple TV or iPad, Aperture albums do not sync properly and you will find that it misses photographs with no warning. This may be an iTunes issue but for me this resulted in the need for me to use iPhoto to build the albums which then synchronised perfectly with iPad and Apple TV.