Thanks for the reply's everyone, very enlightening!
I got this small bit of information from the net:
"Salts from perspiration can eat away at fabrics, causing holes. Avoid deodorants and/or antiperspirants that contain aluminum chlorides. These can cause fabrics - particularly rayon - to deteriorate or turn yellow. To minimize the damage, clean the garment as soon as possible after wearing."
An alternative approach:
Good'ol baking soda can be used by those who like a natural and cheap approach. You may have to wet your pits so it can be able to stick to them.
I don't guarentee that the baking soda will stay on, or how effective it will be, but I did use it a while back for some time without complaint.
Some of my own advice:
Try to shave your pits down to at least a size #2 or #3 (mm), or all down if it suits you. I find deodorant is more effective when its not hanging off a bush of hair. This will also reduce the amount you need as it will work more efficiently being closer to the skin.
My personal opinion is that semi-shaved pits look better. They have a clean kept, yet manly look to them.
I also like to shave mine in a circle to finish them off. This adds the finishing touch for that special 'lady' your about to get it on with. You'll look pro because not many people do this. It only takes about a minute to do, and you probily won't have to do it more then once per week.
And if your going to make love, please don't put too much deodorant on. Keep the amount low if possible. Theres nothing that can break a special mood more than a handful or faceful of deodorant.