My answer would be a resounding, YES!
In my opinion, there is nothing more informative (well, besides reading extensively) than taking the old red pen to someone's pages. I think at times we become so personally involved in our own writing that we're unable to see the flaws. By taking a step back to look at other wip's, you're given a chance to see what works and what doesn't. There's no better learning tool out there and it gives you so many things to take back to your own work.
I recently received some comments from a beta, saying I was being redundant in my writing. Repeating with dialogue/action what I had already shown through other dialogue/actions. I had no clue what to say to it, because I couldn't see it. It all finally clicked when I was critting this evening, and now I can go back to my own wip and snip snip snip to avoid doing the same thing again. (No guarantee, but at least I'm going in the right direction.)
I've learned so much over the past year I've been involved with online forums. I'm still pretty much a spazz when it comes to identifying different aspects of the technicalities, but I'm at least starting to recognize and zap my problem areas. I'm very encouraged by this.