Here is a link to a discussion of dew claws on the retriever training forum. It's long, but it seemed to me the vote was going 2 to 1 for removing them, and quite a few people had experienced problems with dew claws tearing.

http://www.retrievertraining.net/forums/showthread.php?t=80033&highlight=dew+claws&page=3

Personally, I remove dews on my pups. I have seen quite a few pet owners who do not tend to the trimming of the nails, let alone the dews, and it really bothers me to see long nails/dews that are neglected.
I have dogs which I have purchased, with dews, and it is a minor annoyance to me to need to trim the dews, but certainly not a deal breaker in a great prospect!
It is a personal choice, no right or wrong, in my opinion.

Somewhere there is an article supporting not removing dews. Reasons being that removing them weakens the ligament that supported it thereby weakening the pastern. If dogs are going to be worked often in rough terrain then maybe they should have their dews removed to prevent tearing it. Or - if the dews stick out on the side of the leg and are unsightly then remove them. My dogs carry their dews very close to their leg - not unsightly at all - and they use them for a number of activities.

I work my dogs in the field for hunt test training, run them in the fields daily for pleasure and do agility... and have puppies in pet homes that do the same, as well and real hunting. Everyone keeps thumbs here.

If we removed all the parts that could possibly get snagged, twisted or torn, just in case, we'd end up with pretty strange looking dogs ;)

We stopped removing them when we broght dogs over from the UK. They do not remove dews, crop ears, or dock tails. Never have had a problem with a dew claw getting torn.

Read the url I posted. Example after example of dogs injured by torn dew claws, posted by people who saw the injury first-hand.

My dogs do obedience, some at CDX level, and field and the youngest that had the dew claws removed lived to be over 14 with no unsoundness in front. If agility dogs are having problems, I would guess that jumping them on hard surfaces has a lot more to do with it than presence or absence of dew claws. I train outdoors on grass.

I can't figure out how coyotes, wolves, and foxes survive without humans to remove the dewclaws from their whelps if it is such an issue in the field. IMO, breed for nice tight feet, including dews held close to the leg.

When I first started I removed them then I noticed that many kennels were not, we have had our labs in all kinds of rough conditions in the past 30 years and never had a dew claw injury, we have had cut pads and ear tears from going through thick hedge, maybe we should crop their ears. Do what you are ok with, I have seen deformed dew claws where folks did not know what they were doing and messed them up.