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Dogs are unique as guide dogs for the blind- it's amazing watching a blind man get on the bus with a dog; it knows when to get off at a certain stop!
Sniffer dogs at airports for drugs.
Police dogs.
Looking for humans on earthquake scenarios - search & rescue.
For someone who hates exercise having a dog (not as a pet) would force you to walk the dog.

In Islam the only issues are as house pets and when it comes to at-taharah (cleanliness and purity) when licked with its saliva (or brushed with its wet coat)?
I don't know if a dog's and pig's "outputs" are considered "dirtier" than other animals in fiqh or it's all the same.

To be kind to all animals is a must; recall the famous story of a prostitute whose sins were forgiven on giving water to a thirsty dog.

In 2012 there should be a better system of dog walking - it's not nice when owners don't pick it up and you have to walk at night! How joggers cope is a mystery! And peeing at the base of a streetlight - yuk!m

I recall in Spain (maybe other countries) there are special areas adjacent to the pavement for the dog to do its call of nature.

Oh at least we have a custom of taking our outdoor shoes off on entering the house just in case! Worse still if you have a baby crawling around! Some non Muslim cultures (e.g. Japanese) do the same.