I would definitely be worried when a part of the rack is being supported by the glass. The glass on our vehicles is not meant to support racks, or any amount of weight from a bike(s). Like others here, I have had people in the past show up to the shop with a broken back window, and a bike that is simply dangling. One customer actually had their bike come off the rack on the highway, and unfortuantely the bike was run over. Roof racks are good options, and so are hitch mounted racks. You will need a towing hitch on your vehicle...1 1/4" or a 2". The larger hitch will accomodate more bikes, but either are great options. In terms of cost, they are roughly in the neighborhood of a roof system.

Personally, I have a 2" hitch rack that supports either 2 or 4 bikes. I have owned a Hollywood rack for many years, and have used it extensively with)out any problems. Be careful of the companies that are marketing lightweight hitch racks... many of them are breaking and have been recalled.(Thule)