Ditto.
A logline is the shingle above your store. It entices customers to come in, look around and buy something. Make it short, easy to read and understand, but more important make it unique and fresh. Some of the best loglines I believe run around 25 word although I accept up to 35 if done right.
Case in point. 50 First Dates: "A guy has to get his girlfriend, who has short term memory, to fall in love with him each and every day."
There are tons of movies about a guy who tries to get a girl to fall in love with him. 50 First Dates, however, is fresh because of the memory aspect. One sentence can tell the entire story. This is much the case with high concept films, however, low concept (indie dramas) is much harder to describe and takes a lot of work to get a good logline.