I took the MSF after doing ~1200 street Miles on my own. I am a returning rider with quite a few years on dirt, ice racing, etc., so my take on the class reflects my past experience, and may not fit yours.
The class is geared towards folks who've never ridden before. My class was a 2 1/2 day deal; the evening class was a pretty generic meet & greet, and the first day on the range basically covers the rudiments of riding. This included properly mounting/dismounting, finding the friction point of the clutch, brake bias, etc. 95% of the people in my class hadn't been on a bike before, and got a lot out of it. I think one girl dumped her bike 5 times that day.
Day 2 covered so-called 'street strategies', including shifting, lane/space positioning, swerving, stopping on a curve, etc. The afternoon ended with the riding/written tests.
-At 29, I was the youngest rider by at least 5 years. The average age was probably mid-late 30's. All the other riders were harley folks. The class was ~40% women. You think kids have poor judgment? I heard two of the women say "I've never ridden before, and the day after the class is over I'm riding my bike to work because I'll have my license". Whoa, there. I thought middle-aged women would be even more sensible than young guys but there are some SERIOUS problems with that statement. it surprised me to hear folks think that a written permit test and 2 days riding in a parking lot is all it takes to be a licensed rider. Well, they're actually correct for NYS but they're also in for a big surprise once they're out in traffic for the first time at highway speeds. I call this situation a failure on the part of the state license regulation and also the rider. I also think this situation is part of the problem we have with so many M/C accidents every year.
-Everybody passed. This included the girl who dumped her bike 5 times one day, and twice more the next day. In a way it is best that you pull stuff like that in a learning enviroment than on the streets I guess. You only fail if you dump the bike during the TEST. If you fail the test, you can re-take it again (once) for free.
-The riding test was quite simple. I am a little surprised that it did not cover things such as stopping in a curve, where it seems like many accidents are likely to occur but instead focused on low-speed bike control.
-The written test was simple, too. It was a good 'food for thought' test.
-I got 100% on both tests, but then again I should have. Like I said, I am a returning rider. Serveral others got 100% on the riding test. Nobody else got 100/100 like me. That is a little surprising and scary as well because the written test focused quite a bit on street strategy and the riding test on parking lot skills.
-The difference in riding ability between the both days for most riders was both inspiring and dramatic. It was quite a thing to see someone who struggled the first day take off and ride so smoothly the next. There were a couple of 'naturals' in the class, including an older woman who took to that bike like a duck to water. She was dragging pegs with the best of 'em on only her second day riding! The instructors were excellent, and clearly boosted the students' confidences and abilities at the same time.
-A lot of folks expressed their fears about riding in traffic once the class was over. They all seemed to realize that they'd never gotten the bikes over 20 mph or had to do real-world merges/intersections, etc. Luckily many planned to work their way into real-world riding slowly. Nobody who'd planned to ride to work the next day said they still were going to. One actually admitted that riding a motorcycle was a lot harder than she'd been led to believe. Good for her. I don't think I'll be seeing her name in the news any time soon.
-I learned a couple of good things myself, and could feel the difference in my riding ability right away. That made it worth it for me.
Bottom line? I think the MSF beginning RiderCourse is a useful tool for new riders. It does provide a good environment to learn and is not very intimidating for those who are easily spooked. I think the testing is a bit lax and that there are things that should be reinforced for safe street riding that were not covered in enough depth. IMHO this is not the be-all, end-all of learning and shouldn't be considered as 'all you need' to be a good rider. It IS a good place to get exposed to many good riding techniques in a short period of time, however. The rest is up to you (I own a copy of the MSF's 'Guide to Motorcycling Excellence', a separate book from the class materials and available from Amazon.com et al., and highly recommend reading this book in addition to taking the course).
If you have the means to take the course, I say it is worth it. Just consider that course as a tiny part of your learning experience. You'll be learning as long as you are riding; how long you wind up riding is up to you and your judgments/abilities/skills.