Visiting schools is absolutely crucial. However, don't start buying plane tickets until you know your GMAT and thereby your chance of getting in. Once you have a list of programs, arrange a time to visit when class is in session. This is major. And here's why:

I didn't know if I wanted to attend a part-time or a full-time program. My top choice was Berkeley and they had a part time program, so I applied there without doing a class visit. A good deal of my personal network is Cornell so I felt a good degree of attachment there, so I applied to their full-time program. I didn't do campus visits to either. When I finally got around to visiting Berkeley I was on the wait list. I did a "day in the life of" in San Francisco. I visited clients and worked all day, then attended class at 6pm. Everything was good until 8:30pm and everyone started getting sleepy, but the class powered through. We still had an hour left to go and I was falling asleep! I'm a morning person, and taking that visit showed me how unsuited I was for the evening program. Conversely, visiting Cornell made me fall in love with the place: it offered everything I could have dreamed of, and now I'm wishing I had applied to more programs like it, including Berkeley's full-time program.

I was accepted into Cornell and will be attending this fall, but there is still a piece of me that wishes I had visited more schools before applying.