Generally agree that there is a need to re-look at the curriculum in the schools. But I'm also of the opinion that there is a general pool of knowledge that students need to know before they begin solving problems.
E.g. basic maths, physics or chemistry need to be understood before applying them to solve real world problems. The challenge is to identify these basic knowledge. This would be more constructive than just saying PBL is the way to go.
Any suggestions?

Great Introduction to PBL. I am strongly thinking about incorporating it into my curriculum- Industrial Technology grades 8-12.

How might this concept be applied in a high school language arts/English classroom setting?

I was trained in PBL ten years ago through IMSA and am an English teacher in the Hamilton County school system, Chattanooga, TN. PBL works great in EVERY discipline including language arts. I use it to introduce or end a study. If I am using the human condition as a major theme for the literature I am studying, I might start the unit with a PBL on character traits and how they are or are not used today. Usually I have our character education director work with me by asking my students to address the need for character education in the high schools - specific training/classes on this or ways to make students more aware of human behavior. As the PBL concludes, I am able to focus my essential question on human condition transitioning from their prior knowledge gained in the PBL. I use a PBL (mini or major) at least four times throughout a semester. It is a wonderful tool, makes the students aware of many perspectives and allows them to be in charge of their learning. It feeds beautifully into my essential questions. Using the UBD model of backwards planning, I figure out what I want them to know at the end of the unit, and then I plan my PBL and EQ around what the learning outcome should be. I am happy to share some of my PBL's with you. My class has become student driven rather than teacher driven thanks to strategies like PBL, and my students love them.

I have had success with PBL, but rarely using the same project with different groups of students. For example, we are currently working on building bridges from file folders in an Honors physics class, and the students are actively engaged and solving problems. Last year we embarked on a plan to save the Leaning Tower of Pisa. In both cases, we tried the other focus (imagining and solving problems in statics) first, but students were reluctant to engage with the project. I believe that the selection of projects is an inexact science--it needs to be shaped by the nature and prior knowledge of the students. This, to me, makes PBL more difficult, as the PBL-using educator needs to have a whole bunch of arrows in his/her quiver prior to implementing a Project-based focus. Hands on is not always Heads on science!

Has anyone done this with 4th/5th grade language arts or social studies?

I implement project-based learning through planning a literary trip to Boston & surrounding area. Students are given a time frame, money limits, adult-student ratio, etc. I teach American Literature and one year I did this at the beginning, and students could relate back to it when we were going through the Colonial Period and this year I will try it at the end of the year and students can review those literary giants from the Boston area and are reminded of the Colonial Period setting after reading The Crucible. This could easily be transferred to planning a literary-based trip anywhere in the world.
Good luck.

I've been reading a lot about PBL lately, and I really liked what the Buck Institute had to say - which is basically what I think you are saying - direct instruction is still necessary for basic skills. My assumption is that you have to start from the top and work down. Decide what skills you hope your students leave your classroom with and then design a project that aims towards those - assuming basic skills are there, or at least attainable in the course of the project. Also, may be it is a matter or just giving it a go and seeing what needs to be done. Maybe you start with some assumptions, learn you are wrong and build in instructional time for what is missing. Of course, I've only done small projects working towards doing something bigger and I teach in a private school where I have more freedom than the average public school teacher.

Could you explain your literary field trip a bit more? I've been looking for PBL implementations in my lit class and most of what I find is "Well - they write up their findings" and the like.

We are the only gifted magnet school in St. Louis Public School District. Each of our 5th grade Spanish students have been working diligently to create, illustrate, translate, & narrate an original story which we are bringing to you as a podcast.

TPR

The stories are an outgrowth of the textbook we use in the Spanish Language Progam at Kennard. The textbook borrows heavily from the TPR method of teaching, which is Total Physical Response begun by James Asher in the 1920’s. Basically students learn Spanish by acting it out. The textbook uses simple TPR stories in cartoon form. The podcasts are inspired by these stories.

Many, if not all of our students, have ever done much with computers and some heve never even heard their own voices. So the project was in itself a brand-new learning experience in what they can do with a computer. In some ways I feel like a pioneer with a laptop and a few ideas to help make learning Spanish fun and exciting to my students.

We're still uploading our stories online, so we're still anziously waiting to see ourselfes online! Come visit us at kennardspanish.org and tell us what you think!