Depends on what the master's degree is in, and what it's for. If it's to get a master's degree merely for your teaching credentials, then it's on a par with any other master's degree. I've gone 3 routes - I've attended master's degree classes in person (my best learning experience, albeit not in pursuit of a particular master's degree - I just wanted to take those courses during the summer). I've also started one master's degree via distance learning (not really online - classes conducted at one center with students at 3 other centers. That was at University of Buffalo. The program was very new, and I learned ABSOLUTELY NOTHING - it was a complete waste of money (except to have that piece of paper.) To put it in persective, I was taking two courses during one summer session. The teachers decided to get cutesy and apply one of those new fads in education - team teaching. So, they took turns and blended two courses together. One was a technology in education course, the other had something to do with gender issues/family heritage/bullshit. The final project for BOTH courses - 50 PERCENT of the grade in each course, was a ***PowerPoint Presentation***. It had to be at least (*gasp*) EIGHT slides long, and about an ancester in my family & related to my ancestral heritage. I've seen more difficult assignments given to middle school students.
And, the last one was an online master's degree program. After that experience, I don't put a lot of weight on an online degree. Come to think of it, 3 different universities, and all three master's degree programs seemed to be more about the university collecting tuition money than about learning - I would rank all of my undergraduate work - Alfred University, St. Bonaventure University, University of Pittsburgh all as superior to two of the three master's degree programs. Buff State (Buffalo)'s master's degree program in physics education still trumped them all. I believe part of that program has an online component for a few of the courses.