I'm a fan of Adobe Lightroom - its way of working seems to fit my mental model so I find it fairly natural to use. That does depend on you tagging the photos with appropriate metadata of course and not everyone thinks the same as me, so you may not get on with it.

Picasa has matured nicely over the years and has a nice "face finder" that does a pretty reasonable job of auto-finding people in photos and matching them to people you've previously named.

Supporting this I have a fairly simple folder structure of

\photos \ shoot description

Because I rely on tags in the software I don't really need too much hierarchical organisation and IMO hierarchies are the wrong tool for the job anyway because a photo will naturally fit into multiple categories but a hierarchy only lets you express one.

I think the short version of the answer is "Tag everything" - doing it on import isn't that painful and means you can finds it later, but going back through gigabytes of history to add the tags is a soul destroying task.