Power lines are everywhere, you drive under them all day long. There are some people who will not purchase a home if a transformer is located within a certain range of the house. The argument from those who have concerns is the length of time you are exposed to EMF's. I've lived near power towers and have sold near power towers. You will hear differences of opinions. You will have to make a decision on the information provided to you and how you feel about the power towers.
From a lending decision if you are going FHA they do not want to lend on a home if it is located within the fall line of a power tower. Don't confuse tower with poles which carry the lines from one point to an other.
Because of this resale and value of homes located in close proximity to power towers and transformers are affected.
I think the only issue with living close to these lines is that they are not very attractive and block you view to bay trails in some parts of the bay area
You can also get a meter from the electrical company to test a home to see if there is any "leakage" coming in.