When you examine pro bikes, it's very interesting, as it seems that rear lever alignment is team, or should I say team mechanic, dependent. So, for example, TT bikes from Radioshack/Leopard Trek (including Cancellara), Vacansoleil (including Larsson), Saxo Bank (including Boaro), Astana (including Brajikovic) have the QR lever on the rear wheel pointing backwards, as in the photo above. The others have the QR lever positioned under the chainstay pointing forwards (e.g. Team Sky), or back and up, or in the crook between chainstay and seatstay like this:
So, fwiw, here's my opinion. On the rear wheel of CX bikes and commuters that are often parked in racks with other bikes - where there is a risk of snagging the lever - I will orient it tucked into the crook of the seatstay and chainstay. Whereas for TT, I may have it pointing backwards. It really depends on the frame structure around the dropouts and the shape and configuration of the QR lever. I am not that keen on pointing it forwards and down under the chainstay - but I would do that if there is no other way (it depends on the configuration of the lever and type of frame - sometimes it won't go into the crook without fouling the frame, for example). On the front wheel, it's always pointing back, either under the fork or backwards and upwards behind the fork blade. Usually this is achieved with the skewers oriented so that each QR lever is on the left side of the bike.
And yes, I agree with Mr Barry that the quick release is a great bicycle innovation.