depending on how long the specimen has been in the bag dictates how i acclimate. if it has been shipped, i just match temp and add the critter to the QT. the reason is this:
you have a small bag that the fish has been in for a couple of days. altho most shippers usually fast the fish for a few days prior to shipment (ever wonder why there's rarely any feces in the bag?), there is still some NH3 in the bag water, which also results in a low pH. the NH3 in the bag is relatively non-toxic at lower pH values, however, once the bag is opened, the sudden rise in pH causes the NH3 in the bag to become more toxic.
so, for reasonably short durations in a sealed bag, drip or dip acclimation is fine, however, if the bag has been sealed for more than few hours, i don't recommend leaving the specimen in the bag once it's opened.
also, as Bill mentioned, never, Never, NEVER add nasty bag water to your DT or QT. i usually transfer anything that can't harm me by hand. even clams are OK to remove from the water, but NOT sponges.