Ryan Green recently discussed the pros and cons of using child theme frameworks. He looks at a lot of popular WordPress theme frameworks such as Genesis, Thematic and Thesis. It's a great talk that I recommend viewing.
The talk is 43.31 minutes long however the slides that he used in his talk are available for those of you who do not want to watch the video. There are 48 slides in total so it won't take you long to get through them however you should view the video if you have time as it much more in depth.
The above video can also be downloaded in full in MP4 and OGG formats at WordPress.tv.