It has always bothered me that Blogger does not support categories natively. I have suggested this to Blogger Help several times, and I am apparently not alone in noticing that BlogSpot does not have categories.
The Blogger Help article "What other ideas have users sent in?" mentions using del.icio.us for creating categories. I do not like this approach as it links to another website altogether.
One approach I like a lot is Labelr, but it is both third-party and therefore not something I would want to rely on. However, it is very slick. Who knows... maybe Google will buy it up.
I have used a form of categorizing for about a year now. I initially hoped to search by my post title key words but that did not work. Perhaps Google Blog Search was still too young or it was not indexing my blog. In either case, it did not work initially and I gave up on the idea.
It did not occur to me until tonight to search my blog again. I believe I can begin to insert key phrases at the end of my posts for the search to work right.
UPDATE 11:30 PM 03/18: This guy has the same idea, and seems to have a good implementation of it. I think I'll soon be using categories... :-D
UPDATE 07:30 PM 03/18:
UPDATE 11:20 PM 03/19: I think I found the Google search limiter I need... "allinanchor:"