Seems to me the online DVD rental companies have missed a trick here. Given that all communication between customer and supplier is done via the web site, why not make the order you receive your DVRAB more interactive?
For instance, when they receive a DVD back from you, they could have your queue page display a message "the first available DVD in your queue is [for example] No. 7. Do you want us to send this?" If you decline, it could give you the option of having another DVD from lower down the queue, or waiting until a higher preference is available.
Probably difficult to implement but it could make the queue system more palatable than the apparently random way some companies operate it. Because sometimes you want to watch DVRAB in a particular order, and if you can't have No. 1 and then No. 2 you'd rather have No. 15 while you're waiting.