Blogs -- Job posts tied to blogs is a great idea. My job was posted on Joel on Software. My company is about to post an opening we have on there. Turns out our CTO reads Joel on Software. I read Joel on Software. Now we work together. The problem with job posting on blogs is fragmentation. I read a lot of blogs. Not all of them have job boards, but several do. It would be pretty expensive and time consuming to post jobs on all of those blogs' job boards.
RSS -- The Joel on Software jobs board has an RSS feed. I could save a search on there and subscribe to its RSS feed. That was how I saw my job. I read it in Google Reader, clicked on it to Joel on Software, etc. There is definitely no downside to this. Every job site should offer RSS feeds for any job search you can make on their site.