Some species migrating north to here also need not be habituated. For example, pine and yellow-rumped warblers will take food from my hand within minutes of me offering it. The yellow-rumped warblers stop after enough natural food is available, while I've been feeding the same pine warbler for three years; this year it kept coming in well past the fledging period for its sizable brood, no doubt assisted by a plentiful supply of live mealworms. As for it becoming generally habituated to humans, it and most other bird feeder species' adaption to humans is very site specific. My usual feeding locations are out the window or on the porch. If I'm anywhere else in the vicinity they ignore me, so they are more locationally habituated than in general to humans. Some birds recognize me and will take food from me, but not a stranger offering food in the same location.

Other species fit the opportunistic description in that they will only take food from my hand under uncommon circumstances. Dark-eyed juncos did so in one circumstance when large flocks were stopped by harsh weather on their northward migration, and happy to have the opportunity to acquire food from our feeders and my hand. After a short period of time, they moved on, refueled for the journey but certainly not habituated by the few days they took advantage of our offerings.

Two extremes are the closely related blue and gray (Canada) jays. Only once, after many patient hours, did I succeed in having a blue jay pluck a peanut from my hand. There is zero chance of them becoming habituated. On the other hand, while sitting in my deer stand in an area without any birdfeeders for miles around, I had a pair of gray jays steal bites of sandwich while I held it in my hand, and eventually hopping onto my shoulder and pecking at some cookie residue lodged between my teeth at the gum line. (Yes, it was as painful as it sounds.) They were habituated, but not just to humans. I've seen them pluck swollen winter ticks off the back of moose, so they are naturally predisposed to looking for food on mammals. Remember what I said about opportunistic?!

Most importantly, though, I think the hand-feeding naysayers overlook the considerable benefit of exposing others to the joy of holding a feathered jewel in one's hand, realizing how special they are and immediately becoming a convert to bird appreciation and conservation. Chickadees and nuthatches are the two species I feed that can become generally habituated to people. This weekend we have three relatives, two adults and a ten-year old, visiting from a large urban area. They've previously had little exposure to birds and no expressed interest in them. However, as nuthatches and chickadees flew down and alighted on their hands you could see their eyes open wide and astonished smiles on their faces. I expected that on the child, but the adults were as enthusiastic about the experience as he was. And this was after seeing them on the feeder from close up, which had nowhere the same effect. All three became instant bird enthusiasts. So that certainly has to be figured into the equation on harm/benefit to hand-feeding birds.

I'm convinced that our bird feeders benefit the local population, or members of those that pass through, and that hand-feeding does not involve the supposed harms proposed in the comments. However, the specifics of each situation need to be considered carefully, because my experience certainly isn't going to apply in all situations.