Personally, I don't use many people's materials, but I've found two things that were suggested by other people and they've worked for me. Other than that, I don't use things other people wrote, mostly because I know that it's better to write your own stuff.
But is it really bad to borrow things from other people? Well, that depends. It's not really bad to try it, but it's not really smart to continue using something when you know it doesn't work for you. You can always try tweaking it to suit you better, to see if that makes it work for you.
It pisses me off so bad when someone who is Pagan takes on that "holier than thou" attitude and basically tells another Pagan that they're doing something "wrong." So long as you're doing what works for YOU and rings true for YOU, who gives a rat's ass where the info came from?! I guarantee that most Pagans will be able to find at LEAST one other Pagan who does something similar or believes something similar. It's not a crime to use things that other Pagans created, especially if they published it. Don't let any self righteous fundie tell you that you're doing something bad or wrong because Paganism doesn't have "rule book" or leader, etc. You have to do what works for YOU and screw what other people say about it.