smoking while on the pill (google this - or read the instruction manual that comes with the tablets - that's what its for!) increases the risk of:
high blood pressure, so therefore strokes, circulation problems, varicose veins, thrombosis, aneurisms (burst blood vessels/arteries etc.), heart disease etc
some studies also say smoking lowers oestrogen levels, so makes the pill less effective (i.e. the pill is 97-99% effective against pregnancy, so smoking may lower this rate)
smokers also reportedly have heavier and more painful periods
on a lighter note - its all down to the individual. you may or may not develop these problems and it is all down to risk perception. you could be perfectly healthy and not smoke, take the pill and still develop these issues. millions of women take the pill (i do and i smoke) and it is a good contraception to use.
for me, i'd rather smoke, take the risk and not have a baby (the pill is the only method of contraception i can reliably and comfortably use and have done for 10 years now) - if i got pregnant again i think it would be about the worst thing that could happen! as long as you are aware of the issues you can make an informed choice about what you want to do. just be prepared for your gp/nurse to nag you about smoking every time they see you if you tell them!
have a nice holiday!