I am in the same category as you - a hobbyist with about 70,000 images.  I save shoots in separate folders with the naming convention "YYYY-MM-DD_xxxx Title".  I use one catalog and keyword using the magic who, what, where, where and why depending on the image.  With the map module I can likely drop the "where" and the when is taken care of in EXIF and in my naming convention.  You want to make your keywording independent of file location, so it should not matter what you have in each folder.  I would avoid multiple catalogs unless you have a specific reason to create them.

When I go on a trip I create a new trip catalog on my notebook.  I export my keywords from my master catalog and import them into the trip catalog.  During the trip I keyword in the trip catalog.  When I get back, I import the trip catalog back into the master catalog, with any new keywords added to the master catalog.  Then I toast the trip catalog.

I would agree - with an exception ...

Photos for unrelated purposes I keep in separate catalogs ...

1. my photos
2. photos for my church (some are my photos of my church, they go in #1 too, these are kept FOR my church)
3. my son's photos
4. my wife's photos (she wants to see them only, so this is the best solution)
5. my scanned slides from 1970 to about 2000

The first one is my biggest, but the others are not related to it.

i have one big catalog for photos, because i like to search all my photos at once.

when i look for pictures, for example, of my dog i don´t want to open 3 different catalogs.

then i have special catalogs for 3D textures and computer generated images.

i see the reason to organize folders on the HDD after date/time... but i do it for topics.

events

- birthday

   - peters frankenforters 60. birthday
   - lara crofts 33. birthday

- wedding

   - camela and charles parkers wedding

   - etc.

- funerals

- etc.

animals

- birds

   - pigeon

   - etc.

- reptiles

  - etc.

- insects

  - butterfly

- etc.

vacation

- london

  - london 2010

  - london 2012

- ireland

  - ireland 1999

you get the picture.

i do that because before i started keywording that was how i have organized my pictures.
and it helps finding stuff when i need pictures and i am not working in LR.

of course i do heavy keywording in LR.

One catalog (23k).

Folder structure:

 

YYYY / YYMMDD <ShootName>

.....

Film / NNNN <ShootName> (where NNNN film roll number)

Scan (one big folder for old scanned photograhs. I have one, so far.)

Anyone using the bucket system?

Also 1 catalog, almost 100 k images now.

Same folder structure principle.

I am too timid for a real bucket system, especially when I read of bugs biting people with folders of more than 3000 images...

I usually stay below 1000 per folder.

Any other structure such as Agfaclack I organise by keywords & smart collections.

Cornelia

3 catalogs = portability

1) Master - obviously, all images.  Folders by year - keyworded, collections

2) Incubation - photos that require processing. Saved to an export folder when complete and then imported to the master.  If they are intended for resale or display I will import to the presentation catalog

3) Presentation - photos that will be shared externally via web, gallery, print or iPad.  Used primarily as a portfolio. 

Although I'd like to take credit for this system, I believe it was either Matt Koslowski or Scott Kelby that turned me on to it.  The system has served me well for years.