Hello Shorty83,
Oh you've gone and done it now....
http://prepression.blogspot.co.uk/20...ts-of-pdf.html
In short Illustrator can make loads of changes to the artwork (CMYK values in particular) in the background without telling you.
It depends on the work you are printing.
If the PDF was created in Illustrator and saved as a Illustrator Default PDF you should be ok.
A lot of the work I do is Black variable data so not a lot can go wrong (and the bits that do are easy to spot and correct)
Read up on the subject and have a think about the artwork you handle and check out if it's effected or not.