Can poor posture lead to back and neck pain?

Yes it can. The body has been designed with natural curves that allow for your body weight to be evenly distributed through the spine. Your deep core muscles are designed to maintain this upright posture as they can work for extended periods of time without tiring.
When you slouch or sit with bad posture, the forces of your body weight are put through the spine/muscles/ligaments differently, causing stress on all these structures. Long term this can lead to muscles tension, joint stiffness and pain.
This can be helped by stretching, strengthening exercises and treatment to relax the muscles and get the joints moving again.

Best wishes,
Dr David Salisbury - Osteopath - www.bdhh.com.au

As background, actually, much of our posture and the way we move in various activities are complex processes and beyond conscious control due to the intricate ‘wiring up’ of the human body.  Using a crude computer analogy, the ‘software’ – brain, nerves – and ‘hardware’ – muscles, bones, other soft tissues – interact to enable particular programmed postures and movements.  When getting up out of a chair or striking that brilliant golf tee shot, we don’t think about the detailed ‘how’ of the movement sequences; we only think about where we want to go as we get out of the chair, or hitting that little white ball down the middle of the fairway to get as close to the hole as possible.  As a baby develops, particularly during the first twelve months, their brain software runs an automatic program during which they gain basic posture/movement competence.  As parents, we don’t need to teach them how to move; they just think about satisfying their emotional need by using whatever movements their body will allow according to their developmental stage; we are witnessing the gradual development of their anti-gravity system.  
 
As children and adults, posture problems can let us down in a number of ways.  Headaches, an episode of neck or back pain/stiffness, a sport ‘injury’ or periodic niggling discomfort can often be the result of faulty posture/movement pattern sequences.  While some faults can be related to the body having not developed satisfactory posture/movement quality as a baby or as a result of damage to the body software/hardware due to trauma, most often our habits are to blame.  For example, it should come as no surprise that sitting slouched over a laptop or other electronic device day after day eventually takes its toll – technology has made us more mobile, but less active!

For self-help tips, see my response to the question: How can I fix my posture to reduce back and neck pain?

Yes it can.
The most common consequence of poor posture is neck or back pain.
In the lower back and neck, stiffness often preceedes the onset of pain. Over a period of time, poor postural neglect tends to start to produce pain, and the most common cause of this is the disc. 
In the neck it will frequently start as pain at the base of the neck or off to one side. As this worsens over time if will typically refer into the shoulder blade. If negelected for long enough the disc will typically bulge enough to compress the nerve roots that run behind it, giving rise to symptoms in the arm.
This is analogous to the same thing in the lower back, where the progression of the problem will lead to leg pain (known as Sciatica). The neck problem is equally as common although more commonly misdiagnosed (as it frequently mimics a shoulder problem).

The good news is some simple advice can make a huge difference.
Firstly use a lumbar roll when you sit. This should sit at the base of the spine (about where your belt would go). Even correcting the lower back curve with the lumbar roll (called the lordosis) will better align the neck and head.
Secondly get up a move every 45 minutes or so (even 5 minutes is enough to counter the sustained position).
Thirdly support your lower back with your hands and arch backwards slowly and as far as possible x 5-6 repetitions. 
Follow this with 5-6 slow chin tucks (retractions) where the eyes are fixed ahead and you slowly draw your chin back in, keeping your eyes level.
If you did these things regularly your liklihood of developing back and neck problems would be dramatically reduced. 

The Chiropractors Association of Australia recently ran a health promotion during Spinal Health Week that looked at posture in a daily setting and the effects this had on spinal health.

It is worthwhile having a look at what the effects of poor posture are on the spine.

I'd recommend looking at www.sitright.com.au which has plenty of recommendations in regards to posture as well as some great information in regards to what good posture is, and how to sit right.

Hi everybody,
postural stress has become a significant problem now that we are spending a lot more time at computers in the workplace. Postural stress can be evident inn may vocations but the underlying mechanisms of pain are likely the same.
Static postures will create mechanical stress and fatigue over time, this will lead to increased tissue pH and in turn the potential for mechaniacl and chemical nociception. The nociception is the potential cause of the pain the postural stress is the mechanism of loading. Very importantly these processes are not creating inflammation or injury yet; the mechanical and chemical nociception may cause pain which is the warning that if you continue there may be tissue injury.
As discused previously exercise and strengthening increase muscular strength and endurance which can help to limit fatigue and therfore tissue laoding; frequent breaks to rest tissues and decrease the nociceptive mechanisms will also help. Manual therapy such as massage,osteopathy, chiropractic, phsiotherapy etc will all help to manage the neuromusculoskeletal problems that may arise.
Cheers Terry.

YES. YES and YES.  Basically I believe in my 20+ years experience of helping people with back and neck pain, poor posture is the major cause! 
Sit tall and walk tall is my motto with the majority of my patients :-)