I made yogurt for the first time using a recipe from marthastewart.com and I really like how it turned out. The only issue was keeping our little kitchen at about 90 degrees for the 5 hours it takes to thicken. I kept the door closed and oven on (and said a thank you for having utilities included in our rent)...but was wondering if anyone has any experience using the yogurt making machines instead. Seems like a potentially easier way to go about this project. Do they work well?

No experience with one of those machines. Alton Brown showed how to use an electric heating pad to make yogurt on one of his shows. This might be another way to accomplish your task.

I think it was somewhere on Egullet that I learned this method: I heat the oven to 120, then turn the oven off, put the pot in and leave it overnight. Always works fine.