As long as you are up front with the people you are interviewing with, I don't see any harm. There's the rub though; who will want to waste their time to interview you if you have no intention of joining their company?
If you want more money you can talk to your manager but other then that, you just need to get another job. It sucks but that is reality.
The raise-by-counter-offer strategy rarely pays off. You may get your raise but only until they can find someone to replace you.
For companies that are trying to "recruit" you away from your current employer, they are already aware I would assume.
Also, it seems like it would be make sense to deny an offer/opportunity if it's less than what you're currently making and/or vesting value.
I do agree that the counter offer strategy is not always a guaranteed win - I was more curious about people using this as a way to find out their "market value" (what someone is willing to pay/offer you)
