SHAPES/ CIRCIUT TRAINING ?????

wHAT ARE YOUR THOUGHTS/KNOWLEDGE/EXPERIENCE ON CIRCUIT TRAINING ???? There is this new gym in my area that I went tocheck out - it is very nice but I have never really been intrested in the shpes circuit training thing . I just wonder if you are switcing machines every one to two mins how effective can it be ??? I am very comfortable with the eliptical machines at my current gym but then again that has not really gotten me far either - i am considering changing becasue latley you always have to wait for machines at the ymca and the new help is not as friendly as the old help was and I find my self making up anything not to go -- I have found and heard that this new plance is great and supportive but that they only do circuit training ....... any thoughts ????