After installing junkfilter, I can now see what percentage of my spam is caught by my original rules and what percentage is caught by junkfilter. My filters catch about 8 messages for every 2 that junkfilter catches... but looking at the junkfilter messages, I realize it would've been really difficult to filter it the way I've been doing things. Compare the sizes of my procmail recipes vs. junkfilter's ... mine are about a page long. Junkfilter's are 1,500 lines long. Mine are about 100. So, consider that 1/15th of the code does 80% of the work... of course this isn't always the case with every problem, but clearly it shows that there is a basis to the maxim "it takes 80% of the time to do the last 20% of the project".
I don't want a somewhat good solution --- I want a perfect solution. I don't want to see a single spam message ever, and I don't want to see crappily laid out web pages ever.