I've installed the reCAPTCHA plugin for Wordpress today. The whole process is very simple - took me less than 15 minutes. Simply follow the instructions on the download page. I like reCAPTCHA because not only does it help to prevent comment spam, it helps digitize books as well. I don't know how it works exactly but the basic premise is that words are scanned from books and used in the pictures for reCAPTCHA. How the system tells whether the entered words are correct or not, I don't know. All I know is it works and that's good enough for me.
Another thing that I've done is implemented 'nice URL'. The URL of the post now shows the year/month/day/title instead of some odd-looking question mark combination. I've done this mostly because it helps other people linking to my pages and also search engines indexing my site. The whole thing is quite automatic if your server is configured for it. The only thing to note is the make the .htaccess file writable.