Pros
Cleaning windows can be a lot of fun. It is easy to have a flexible schedule. This is a good job for artists, students, or others who need flexible, part time, inconsistent work. The people you work with are good, fun, hard workers. The owner is honest and open, and committed to the highest customer satisfaction. The customers are almost all great people, but if there is a problem, the owner doesn't leave you out to dry.
Cons
There is very little work from January to April. You will learn all you are going to learn within a year. There isn't room for advancement within the company, and working there doesn't necessarily give you many transferrable skills.