Like the unlined Carhartt work pants made of the same washed duck, these have outstanding wear characteristics.  They look darn good, too.  I got a pair of these to supplement my unlined pairs of the same pants for those chilly days when I have to work outside when it is cold.  Here are some points of observation based on my wear:

Pros:

*  Tough - Carhartt washed duck wears like ballistic tent canvas.  Where my denim jeans have been worn to tatters with holes in the knees, these pants keep going strong.  The fabric is very good at resisting tears and abrasions.  Some of the conditions I've thrown at it (kneeling while working):  gravel, dirt, asphalt, concrete, and composite roof shingles.  I don't own a pair of pants that last longer and wear better under heavy work conditions.  Period.

*  Comfortable - You'd expect that these would be stiff enough to stand on their own given how they wear.  Not so.  These are comfortable pants.  While heavy, the fabric is also soft.  The unlined version is plenty comfortable to wear even in the heat of the summer, but these flannel lined pants keep you warm in the winter.  The construction of the pants make them very comfortable to wear when you are actively working - this is especially important if you have to do a lot of kneeling, bending, or climbing for your job.  I am a contractor and these are very comfortable to wear all day long.

*  Construction/Quality - The zipper is a heavy brass YKK unit that operates smoothly, and the button is likewise heavy.  Utility pockets are sensibly sized and placed, as if the designer actually used them to carry tools, rather than imagining so.  The hammer loop is wide and will accommodate a full-size framing hammer.  Nice.  Seams are double and even triple stitched in areas of stress, complementing the fabric with equally sturdy fit construction.  Front slash pockets and rear pockets are likewise well made and generously sized.  There are seven belt loops, providing good suspension if you load the pants down with tools, and they are wide enough to fit a heavy leather belt.

*  Warm - These are flannel lined, after all, and they are superb at keeping the cold at bay.  Though the flannel doesn't seem to be very heavy, these are warm pants and are effective at keeping the wind from cutting through the fabric.  It would have to get really cold for me to break out the long johns to wear with these.

*  Sizing - I find the waist to be true to size, though the flannel does make these a bit more snug around the waist than the unlined pants.  I'd say if your regular size is on the tight side, err on the side of caution and add an inch to the waist when getting the flannel lined version.  I really like the cut of the legs on these pants - they are roomy without being baggy, making them extremely comfortable to wear, especially on the jobsite when a lot of movement called for.

Cons:

*  None to date

Other Thoughts:

*  Styling - These don't have a lot of styling cues that some other work pants attempt to add.  As work pants, they don't need it.  That being said, I think these are good looking and - unless they are covered with grime or dirt from the job - I don't think twice about using these for casual wear, going to the bank, picking up a bottle of milk on the way home, etc.  The choice of colors is limited, but I do think the colors that are available complement the nature of these pants.

*  Cost - I always seek value, without regard to cost, and I think these pants offer up solid value at non-sale prices based on their quality, utility, and longevity.  Get them on sale, though, and they represent a steal.  I got my last pair for twenty bucks which I consider to be silly-inexpensive for these pants, and I wish I'd bought a few pair.

If you work outside in the cold and you need pant that are as warm as they are tough, these are for you.  These are what you want to wear when you are out on the woodlot, cutting down trees and chopping firewood in the January snow.  They also happen to be great casual wear for a cold weekend out in the yard or at the ballgame...  Recommended.

*** UPDATE 01/23/12 ***

Something to consider if you plan on wearing these while working on a sloped surface, like a pitched roof:  When kneeling, the flannel lining will move against the outside fabric.  On a roof, for example, this is slightly unsettling.  Unlined work pants allow your knee to 'set' against the fabric if you are kneeling on an inclined plane, but these lined work pants work a little differently - as I discovered putting a new roof on my garage before the rain came this past weekend.  I stand by my rating, but I thought I would add this latest experience to my review.