With respect to my colleagues, there is no one program for everything. I like iPhoto a great deal for both photo management and simple clean-up duties, but I mostly round-trip things from there in to Photoshop and back (this a built-in feature of iPhoto). When you get into the really large photo libraries, Apple's Aperture or Adobe's Lightroom are aimed at people who are a little more serious in the photography than I am.
Pixelmator is a great little graphics program (and inexpensive!) that does a number of things PS does but it's not really Photoshop and not the best choice for serious photo editing due to its inability to use PS plug-ins. Elements has the ability to use some PS plugins but I really loathe the way it tries to take over organizing your photos.
ACDSee Pro for Mac (disclaimer: I used to work for them) make a great program for people who prefer to avoid the "vault" (ie program-assisted management) of their photos, and it has *insanely* powerful batch processing capability, EXIF/IPTC editing, and amazing editing tools, but again it's no Photoshop.