If you really want to have the quickest access to your photographic works, a hierarchical storage structure is not really going to solve the problem. Hierarchical storage structures are great for physical project organization and historical/archival purposes, but they do not lend themselves well to "finding" your work.
Most professional photography tools, such as Aperture or Adobe Lightroom, allow you to add a fairly extensive amount of metadata to your photos. Metadata is information about each photo, which would include the standard stuff like date and time, camera equipment used, possibly a GPS location, etc. In addition to the standard stuff, you can also add your own metadata. This includes standardized fields like IPTC properties (artist, title, label, etc.) as well as generic properties which are usually called tags, keywords, or categories.
Adding metadata should generally be done up front, and in tools like Aperture or Lightroom, you are often able to create prefab sets of metadata or manually enter common metadata that can be applied to everything you import from your camera or memory card. Common attributes like "Mountains, Sunset, Vacation to California" can be applied in bulk like this. After import, you will probably want to work through your import set and fine tune the metadata for each photo. To lighten the workload, at the same time you can decide which photos are "keepers" and which photos are "discards", and which may be neither, and only focus on adding more specific metadata to the keepers.
By adding metadata and keywords to your photos, you now have a dynamic (rather than fixed, as would be the case with a rigid hierarchy) way to search your photographic library to find what you need quickly and with little effort. You can usually search by any EXIF (camera hardware, date/time, location) or IPTC (artist, title, copyright) metadata, tool metadata (rating, color tags, edits applied, etc.), or custom metadata (keywords/tags/categories). Many tools offer a way to create saved searches, sometimes called smart collections or smart libraries, to save search criteria and quickly find any photos with the specified metadata.
Apple Aperture should support most if not all of these metadata features, and allow you to search your library to find any set of photos you want in short order. As to exactly what metadata you add to your photos...thats up to you. Organize your work in a way that best works with the way you think. Finding what you need should be a synch after that.