I've done occasional workshops, and have found them valuable in terms of understanding my own creative process. I primarily learned most of my photography in art school. I find it, at times, quite helpful to come together for a weekend workshop to look at and talk about my work, and the work of others. I did one week long workshop in Maine about 5 years ago, and found it propelled my work forward in a way that I had not imagined it would, but I also felt after, that I really don't need to devote quite so much time and money to workshops, so I've only done about 2 shorter and less expensive workshops since.
I must say, like others, there are a lot of workshops out there that look to be a total rip off, and I would simply say, buyer beware. The best education will far more likely be found in an accredited university, and not by cobbling together an education through a lot of workshops.