The image at right is from a full-page ad touting healthier Happy Meals. That is appreciated, McDonald's, but summer need not be capitalized. Lowercase summer, spring, autumn and the like unless they are part of a proper name or formal title. Some examples:
My mother loves fall colors.
The Fall 2012 semester begins in two weeks.
I loathe winter weather.
I'm going to win a gold medal at the Winter Olympics.
In the spring, I look forward to the hot, hazy days of summer.
I attended the Tempe Spring Festival with Summer Sanders.
I hope this helps to clarify the issue. It's open season on improper capitalization. Hunt for misuse.