First we need to start with the canon facts we have for Daniel. The, presumably, only child of Claire and Melbourne Jackson (canonly stated no sister, presumed no brother since it's been six years and we've never heard of him) was orphaned at the age of eight when his parents were killed in an accident. He witnessed their deaths and was likely put into foster care when his grandfather chose not to take responsibility for him.

Not much of Daniel's life from the age of eight to the age of thirty is really known. He studied under Dr. David Jordan and likely studied with and formed a relationship with Sarah Gardner, Steven Raynor and, either then or at another time, Robert Rothman.

We also know that he spent time in the Yucatan and Wales.

It's been widely speculated that Daniel was abused in some way while he was in foster care, yet there's been no canon information given to support that.

Family

 Daniel really has no family, apparently just a grandfather. And it's this same grandfather who chose not to adopt him after his parents' death so it's presumed that the young Daniel became a ward of the state of New York, since that's where they were when his parents died. (It's highly unlikely that custody of him was given to another state, so he probably grew up in New York State, possibly New York City.)

I see this as making Daniel very independent, mentally, emotionally and physically. I personally don't buy into the abusive childhood belief, but I do think that some of the behaviors of adult Daniel do have their roots in his childhood.

Adult Daniel sometimes loses his compassion in the face of scientific discovery. In Broca Divide he was willing to allow a woman to be raped before interfering in the 'natural' way of life of the people. His willingness to allow Sam to 'go along' with the Shavadai mode of dress nearly got her killed. He's much like Sam, getting scientific tunnel vision, sometimes only seeing the human toll when it's pointed out to him. He also tends to focus on short term solutions, sometimes needing to be urged to look beyond them and recognize the long term ramifications of his actions.

I also see this sense of emotional detachment in how he's willing to abandon his home and leave, dropping everything to just go and move on. He did this the first time in the Movie, first blindly following Catherine and later staying behind on Abydos. He also did it in Meridian when he ascended. While his physical condition obviously had something to do with his decision in Meridian, in the Movie he literally turned his back on his home and home planet and chose to stay on Abydos. This suggests to me that he doesn't seem to have a deep emotional connection, even to family or co-workers. This could be a rather common phenomenon among with orphaned children, the lack of parents enabling them to become more isolated in their feelings and emotions.

I think this does effect how Daniel treats his friends, often coming across as brusque or uncaring. I don't feel that there is any maliciousness in these actions; they're just a product of a young man who was raised in emotional isolation and whose sense of empathy may not be as fully developed as others.

He also is a highly intelligent man and often exhibits frustration or exasperation with those that aren't quite as smart as he is and that can't 'keep up' with him.

Career

In canon, Daniel is stated to be a Doctor of Archaeology. He's also shown training and skill in linguistics and anthropology. Chances are he spent much of his adult life working on digs in various places in the world, stated in the Yucatan and most likely Egypt (given his knowledge of Egyptian mythology and artifacts). I would think this would lead to a very transitory life style with him either not having any real home, or home just being a place to keep 'stuff' while he's away for weeks/months at a time. This would seem to further suggest an emotional detachment, 'home' being where he happened to be at a given moment in time.

Daniel is definitely a leader in his field. Even in relative disgrace he had enough clout to fill a lecture hall.

The fact that he had the strength of belief to openly decry accepted 'rules' about archaeology speaks a lot for his inner strength. He's not a person to let his friends or co-workers define who he is and what he believes; he will speak his mind, not really caring if others agree with him.

Again, this suggests an emotional detachment by not allowing current beliefs to define his own, but it's also an example of strength of beliefs. In this case, emotional detachment is a good thing; he's not intimidated into following the norm.

His career seems to have pretty much ground to a halt since his joining the SGC. In Crystal Skull, Nick says he hasn't published in two years, and not publishing a paper is a death knell to someone in the archaeological field. It's the equivalent of an actor not having made a movie or appearing in anything for two years… basically a retirement.

His focus is apparently 100% on the SGC and the problems with the Goa'uld. He's places thwarting the danger to Earth ahead of his career. As have other members of the SGC, Sam for example.

The bad thing about this is, unless the Stargate becomes public knowledge, Daniel's career is pretty much at a standstill. Even studying on Earth, he would never be able to quote facts learned off-world to support his theories. This may be why he's not focusing on his career in any way.

Future

Daniel's immediate future has yet to unfold; we have no real indications of the effects his ascension and descension will have upon him. It will be a little like a normal person's brush with fame: to some it's a positive experience, and to others it's often very detrimental. Only time will tell.

It's also very possible that Sarah Gardner will play a part in his immediate future. It's already been established that he feels responsible for her possession by Osiris and that he wants to 'fix' it. Will this lead to any romantic entanglements?  Also, only time will tell.

Daniel's career, as stated, is pretty much at a plateau. It's now been about four years since he's published which means in the academic community, he's virtually a has-been. This could change in an instant, however, should the Stargate become declassified. He would likely rocket to immediate star status, as would many of the other involved personnel.

Daniel is not perfect; like all of the others, he has his flaws. He can be obsessive, insensitive and, at times, arrogant. However, he also is capable of fantastic leaps of intuitive thinking and is able to find common grounds, often being more open minded to differing life styles and behaviors.

Daniel has changed over the years, losing some of his naiveté and becoming a more active participant in the team. He still has his principals and beliefs, but has also opened his mind to other ways of thinking, I feel making himself a more rounded person. It will be interesting to see if his time spent in 'glowville' will result in further growth and a differing attitude.