I was curious, so I looked up what the AKC has to say about BC temperment. Here's what I found (I added the highlights):
The Border Collie is a workaholic which thrives on
mental and physical exercise. That is the good news.
The bad news is that these are the very traits that can
make him difficult to live with. A fenced yard or
enclosure is important to keep your Border Collie safe.
Traffic is especially hazardous for this breed, since the
dogs may tend to try to herd cars if not kept out of
harm's way. A fenced area will not provide enough
physical exercise, nor will a walk around the block and a
few tossed balls. Boredom is the source of many
behavioral and training problems. A Border Collie that is
alone for long periods of time may tend to develop
compulsive behaviors such as chewing or digging. This
is not a dog that will happily lie in a corner and watch the
world go by. In addition to being intelligent and eager,
as a breed they can be inventive, strong-willed,
independent, territorial, and manipulative. They are
driven to participate in as many family activities as
possible. It is up to you to make this constructive.
Performance activities such as herding, agility,
obedience, daily running, biking, or other outdoor
activities can help provide the physical and mental
exercise a Border Collie requires. It is appealing in a
thirty second TV commercial, but this dynamo can be
frustrating in some pet home environments.
The Border Collie may herd moving objects and people.
When misdirected towards cars, children, bicyclists,
roller bladers, cats, squirrels, rushing water and any
other moving things, the Border Collie's herding instinct
can be a problem for the entire neighborhood. Most
Border Collies react very quickly to stimulation, which
can make them sensitive to sudden sounds and
movement. Although they can serve as enjoyable
companions for mature well-behaved children who are
experienced with animals, Border Collies may find the
noisy games of younger children disturbing and
over-stimulating. This may evoke inappropriate herding
behaviour, even including nipping, on the part of the
dog.