My Take
I like IXL because it ties the math curriculum into the website very well and provides a huge amount of reporting to see student progress. Also, it has immediate feedback and provides a brief tutorial for students if they miss a problem. However, some students don't take the time to read/think about the tutorial information and just keep guessing at the problems. The differentiation is nice and easy to implement.
How I Use It
I used this website teaching a 7th grade math class. It was a great resource for practice and reinforcement of skills. Once a week I gave the students 20 minutes of class time to work on section(s) I specified. I provided homework passes for students who met time spent/percentage correct goals to encourage them to use the program at home. Walking around the classroom as they worked allowed for one on one instruction/review of problem areas and the reports helped identify pacing of curriculum in class.