I've suffered from carpal tunnel due to keyboarding so bicycle ergonomics interests me. Finding a comfortable balance between an forward and an upright posture would depend on what task you're trying to achieve. I have 5-inch risers on my extracycle, but a 2-inch drop on my road bike sporting butterfly bars. From what I've read, basically your core strength and not your shoulders should be keeping you upright. Choose a sweep and grips on your handlebar that keep your arms reasonably straight, comfortable and neutral. If you're leaning on your wrists for hundreds of miles, you might be damaging yourself. On my risers, I choose ergonomic grips that I tilt to support the edge of my palm, and my brake levers are oriented to keep my knuckles oriented in a straight line to my wrist and elbow.
An alternative to flat or riser bars that might provide some variety in posture are butterfly (aka touring) bars (like a figure eight). These can be fitted with flat-bar equipment or drop bar equipment (depending on what brakes you have, if you have V-brakes, that means you want cyclocross style long pull drop bar brakes). I ride a Trek 7200 with integrated brake-shifters from the original 1"-riser bars mounted near the back of the bars. I use the back of the bars to get a more upright posture, and the front of the bars for an aero posture. I can tell I need to adjust the brake lever angle on the butterfly bars, I'm flexing my wrists too far forward.
In "It's all about the bike" by Robert Penn, the author is coached to set handlebar height to what angle he can hold his fingers lightly on for a time without leaning on the bars. Leaning on the bars could lead to shoulder, elbow and wrist strain.
Having ridden almost only flat bars or butterfly bars, I am becoming more open to the notion of drop bars. I believe that "Dirt Drops" are wider and shallower, intended for less areo and more steering leverage as appropriate for cyclocross.
Here's a page showing butterfly bars. Livestrong has a few good paragraphs on handlebar fit. Also, I find lots of discussion on handlebar sizing on bikeforums.net as well.