HI C.,
I had the same worries when I first sent my 2 year old to daycare. I was terrified. After I dropped him off the first day I thought to myself " what have I done, Why did I just leave my child alone with strangers lol. However, it does help if you take your time looking for a place that you and your child can feel comfortable with. Take your son to all the places that you interview to see what his reaction is and if he feels comfortable. It also helps if you know someone who has their child at the same place. I was referred to my Son's daycare by a cousin whose daughter was also attending. When I took my son in for the tour he did not want to leave. But be prepared for at least 2 to 3 weeks of crying when you leave your son. I felt really bad because everytime I left my son the first couple of weeks. He would cry and I'm sure he was wondering if I would ever come back again. It took some time before he was okay with me leaving him.
As far as bad habits go. I don't think that my Son has done anything that he would not normally do. My Problem is that within the first 4 or 5 months my son was sick all the time. He was constantly catching colds and even came home one day with pink eye. before Daycare my son was rarely sick. Last winter was the worst I was sick, my husband stayed sick as well as my younger baby. I think the worst is the illnesses and the germs that toddlers pass back and fourth. So, now its been about 4 months since my son has been sick so things are looking up.
I'm a full-time working mom. So, I feel that my son's daycare has been a big help to me with getting my son to sit on the potty. He has also learned his ABC's, Color's and numbers. His speech has also improved. He is saying prayers before eating. Also, My son was never around children his own age before daycare. I think that exposure was good for him. And I believe that there are more polite well mannered kids in his school than those who are not. I feel that maybe if he was home with a relative all day he probably would not be as "educated" as he is at this time. We really only have the weekends to spend much time together. When I get home from work we basically have a few hours together. We eat dinner and get ready for the next day.
Sorry this is so long, but just realize that your child will have to go through an adjustment period. And if he is in a quality daycare setting (one that does not just watch kids but teaches them too) he will thrive.