[Andrew999]

Miss Masque was fun – remind me again why non-flying superheroes wear capes – don’t they get in the way and run the risk of the villain grabbing you by the cape from behind? Do they have secret pockets – is it somewhere to store your sandwiches in case you feel peckish on a mission?

Link to the book: America's Best Comics 25

[The Australian Panther]

There is a simple reason why Superheroes wear capes, they look great when you draw them. An artist can add a lot to the mood information on a page by using a cape.
Yes, in reality they would mostly be a nuisance.   

[SuperScrounge]

remind me again why non-flying superheroes wear capes

[crashryan]

During the Zorro craze a playmate talked his mother into sewing him a Zorro costume, complete with cape. During the next 15 minutes of swashbuckling, he tripped over the cape so often that he took it off and never put it back on. One must be agile indeed to wear one of those things in action.