Chris is correct. Too much conflicting information here.
Plus per an earlier string of posts, too often DYIers get into projects that are just beyond their capabilities.
But per my original response. Yes, it definately can be done. If done correctly, you will not have some catastrophic failure in your house. Again, that is IF DONE CORRECTLY.
I did state that I had done it myself in my prior post. I also have a degree in Mechanical Engineering. I have knowledge on truss design, etc. I designed my particular installation, and had a good friend of mine that is a carpenter help with the installation. It truly is not that difficult for a pro, we completed the installation in a day. BUT.....it could be disasterous for a DYIer.