Even though they are a bit out-of-date, I love the series by Ames and Ilg, the ones titled "Your Four year Old, "Your Five Year Old" and so on.
My dd is four and I have definitely noticed that she has turned into a big kid in the past year. She doesn't get an allowance, and I'm not teaching her to read, but she does have some responsilbilities around the house - cleaning up her own toys, bringing her dishes to the sink, helping me with the laundry or shopping, etc. I wouldn't worry too much about this, but i do beleive that helping with the day to day stuff teaches children how to be contributing members of the family, and it also makes them feel good!
The most significant change I have seen over the past year is the importance of friendships. At three, she enjoyed the company of other kids, but at four, she NEEDS other kids to play with, so they can make up their stories and act them out, or be silly together, or whatever else they do. I don't know if you plan on sending your child to preschool, but if you do not, then arranging play dates and joining some classes or just going to playgrounds and encouraging her to make new friends is a good idea.
Don't panic, by the way!