Not only are Clark's comfortable, but they are also extremely durable. I have two pairs of browns and two pairs of blacks that I rotate -- I must have hundreds of miles worth of walking on both and they are still holding up great. Each pair is on 3-5 years of use in daily rotation.
Other shoes I've had (especially from designer brands) have soles separate from the uppers, threads come undone, holes wear through the sole, etc even after a few months of wear.
One problem is Clark's doesn't really market anything (in the US anyway) that would be considered really dressy (for wearing with a suit). Instead they are mostly dress-casual shoes, and the Clark's stores push Bostonians for the dressy line (for wearing with suits, for example).
I'm going to try some Bostonians soon.
--Chris