Basically salmeterol (albuterol in the US) does not treat asthma - it
merely reverses one of the symptoms.  So there is a risk that the
medicine can 'cover' deteriorating asthma until it gets to the point
where the patient is in serious danger.

The rule of thumb to use id that if you are using salmeterol more than
three times a week - you need to be on other medications that will
actually control the underlying disease process.

"...there is always a well-known solution to every
human problem--neat, plausible, and wrong."
  H. L. Mencken

Well, first of all - that shouldn't be an issue since Salmeterol is
not normally a medication that is increased when you are having
increased symptoms. The normal dose is twice daily and there is not
much adjustment that is normally done.

The warning stems fromt he SMART trial. The kids that showed the
increased risk of death on Salmeterol were poor black children
(interestingly - not the poor white kids - make what you will of it)
who were at baseline poorly controlled and had a low usage of inhaled
steroids.

My interpretation of this study (shared by every expert I have read on
the subject) is that if you have poorly controlled asthma then just
covering up the symptoms with Salmeterol rather than treating the
inflammation with inhaled steroids is a bad idea. If you are on
inhaled steroids or have some other condition than asthma (like
COPD/emphysema) then the results of this study (and hence the warnings
that stem from it) probably do not apply to you.  On the other hand -
if you are having poorly controlled asthma while not on inhaled
steroids and the response of your doc was to just prescribe salmeterol
then you probably need to think about that.

Your doc should be giving you guidance - preferably in the form of a
written plan - on what to do if your symptoms worsen.