it's definately a good idea!!! but you have to spend some extra time planning.
I did 5 (yes, five) in one week--although I was sick of being in an airplane, living out of a suitcase, and eating continental breakfasts, I think it was a REALLY good choice, and would do it again if i had to.
not only does it minimize how much school/work you have to miss, I also think it helped my be mentally on my game at interview time.
It allowed me to have basically one "preparation and stressing" session starting a few days before, rather than a bunch of 'em spread out over a semester.
If a question threw me off or if something didn't come out the way i wanted it to, i would, like pretty much anybody, think about it over and over that night and how to answer better. And then the next morning, i got to put those "improvements" to work immediately rather than let it sit and for several days/weeks/months and forget about how i wanted to word/say somehting.
definately schedule them back to back if you can. it does take extra planning (like how/ in which city you'll do dry cleaning if and when you need it? etc.)