I'm finally getting around to keywording my library of stock images. What have you found is the best way to assign keywords? If I simply input hundreds of keywords this list gets rather longer. Should I be using subcategories to group keywords? ANy tips are greatly appreciated. 
I dunno, but when you find a good system can you let me in on the secret? 
I avoided keywording in the past, because it's boring, and because Bridge had bugs making it difficult. Nowadays, I have more photos, and I'm running out of excuses.
I originally tried keywording everything in an image, but I found that this created too much work for little benefit. Now, I just keyword the location and the main subject.
To make things more manageable, I have a 2-3 level hierarchy, which I can expand depending on the topic. I also have the option set to tick parent categories. Locations start with the country, followed by the town. People, start with "people", followed by friends, family, organisation or crowd. Animals start with category, etc. etc. This seems to work okay for me, but I think it's a very personal thing.
The trick IMO is to just do it, and keep it simple. You can always refine it later.
