I moved from iPhoto to Lightroom (though I understand that LR an Aperture work on the same principle).
First of all - it's really important to let the program manage the location of the photos - not Finder. If you decide to create a complex folder structure, do so using the program. iPhoto, Aperture, and LR use a database to manage things. If you use Finder to move photos around then the database can lose track of where the images are.
Using a complex folder system misses the whole point of Aperture and LR (iPhoto is a bit different). My suggestion is to let Aperture and/or LR create their default folder structure which (for LR, at least) is Year-Month-Day.
Then use the keywords to tag the photos into places/projects etc. Or use the Collections/Albums for projects/places. Then use keywords for content. Once you have figured out the fast way to tag and/or move into Collections/Albums you should find that it takes as much time to do it this way as moving images in specific folders. For instance, in LR, you can set the keywords on import, meaning that there is no extra steps after import to move the images into a folder. I assume Aperture is the same.
The problem with using a complex folder structure is that you are relying on memory. If you have gone to several cities in Europe, taking photos of statues, fountains, and cars - and then set up a set of folders by country and city, and then sub-folders in each for statues, fountains, and cars how do you file an image of car in front of a statue? Or a statue in a fountain?
And then, if you want to show someone of that cool Renault in front of the Tivoli fountain you need to remember in which city you were, and then where you decided to file it. Assuming you remember that it was a Renault and not a Saab.
The advantage of keywords is that I could simply search on "Car" and "Fountain", and be presented with all images of both regardless of the city. Or if remembered the country, but not the city I could add that and narrow the search even further.
In LR (and I assume Aperture) you can set up a smart collection that is essentially a saved search. So, as you tag your images the collection is updated as automatically. So, a collection can be set up for "Renault". And/or for "Renault", "Fountain", and "Europe". etc etc
Where you save a lot of time is in several years when you only have a vague memory of an image. You just do some keyword searches until the image pops up. Or, failing that, you can just browse all of your images in a grid. Sometimes you need to see the images taken at the same time to find the image you want.
If I recall, iPhoto is different because it actually hides the physical structure (at least by default) of the folders from you and presents the "virtual" folders. You can, iirc, drag a photo into as many albums as you want. I think it can be said that iPhoto actually uses 2 keywording systems. One is the actual words that is uses for what it calls "keywords", and the other set are the albums. Albums can be thought of as visual keywords.
Hope this helps.
