I've been using one for 2+ years now (I believe it is the Noah(tm) fabric) which has done a good job on dust protection (until now, I've only used it in the garage). Having the cover greatly extends the time between washings if you don't drive the car every day.
One recommendation: I didn't realize until after receiving the cover that it was not machine washable. This is a big deal, try to make sure the one you select is. If I were to do it over again I would probably just buy a cotton/flannel cover for my application as I don't need the weather resistance - I had intended to cover the car while at work, but this has proven impractical in my opinion.
I can't tell you the number of times I've ended up very thankful for the cover being on the car when something has been bumped in the garage and ended up in contact with the cover and not the car!
BTW, I did a fair amount of price shopping at the time and Tweeks' price was very competitive for a custom-fitted cover. For example, JC Whitney didn't have a better price for the same style of fabric. The Porsche cotton/flannel cover can be found on special periodically - and has the benefit of a nice Porsche logowhich you can look at when the car is covered. I think mine just has a Fox on it...
