Definitely one of those love it or hate it items. I'm in the 'hate it' category.
Got some as a gift some years back. Gave it a try. Stuff stuck worse than it ever has in a regular pan, no color or crispness to the crust. They're difficult (read dangerous) to pick up because they're so flimsy and the instructions say not to put them on a cookie sheet for baking. When your stuff sticks to them, you can't use anything sharp to pry it out. You can't (according to the instructions) spray them with cooking spray to avoid the sticking. Just too many negatives from what I experienced with them. And the pieces I was given were one of the top brands in that stuff.
And on top of that, there are serious health concerns being discussed regarding cooking silicone.
Did find one good use for the muffin pans, though. I line them with cupcake papers so my food doesn't touch or stick to the silicone, and use them to make individual cheesecakes in the microwave (only takes 4-5 minutes nuking time).