I have to point out that Photoshop CS 5.5 (et al) is, you know, $600. Unless you are a professional photographer, that's probably a bad cost-to-benefit ratio. Especially when you can spend well under $100 on either Pixelmator or Photoshop Elements and, in concert with iPhoto for management, have 99.99% of consumer photo-editing needs met very easily.
I'd have to agree with Chas here. Full blown Photoshop is quite the bit of overkill for a "photographer" if all you need is management plus editing and then perhaps something on the side for stitching and maybe the type of cloning that goes beyond what Aperture or Lightroom can do.
PS is great for someone who is more into taking a photograph, and turning it into something totally other than what it actually is. At that point, it's not so much photography, as it is "creative artistry" or whatever you want to call some of the over the top stuff that some people like to create.
I'd also like to wholly disagree with those who say that Aperture or Lightroom is limited. I can achieve the results that I need to in order to sell fine art or museum print photography with Lightroom. Aperture could get me there as well, if I preferred it but I don't. And Aperture in fact, has better cloning capabilities than LR.
I do have PS, should I really want to work with it, but I really never want or need to. Layering is cool and the tools in PS are great, but I just don't have the patience (or time) for it anymore. I don't need to make things magically change places, or create things that weren't ever in the scene in the first place. To me, that's pretty cheesy. As a photographer, I much more enjoy telling a story about where I am, and having that story come through as true to life as it can through the lens.
That's all I need.
For the $ I'd second PSE and maybe Bridge for keeping it all together if you don't need database management. But believe me... you WILL probably want a better form of management beyond iPhoto or Bridge at some point.
Doug