JB,
Tea and coffee stains usually don't need bleaching kits to remove them...they could just be easily removed by regular scaling then polishing.
Bleaching pastes are composed of two main ingredients Hydrogen Peroxide and Flouride...sometimes you would also find abrasives if you use regular tooth paste with whitening power!!!
I personally don't recommend bleaching...but I can't forbid it at all becasue in some cases they could be magic..So i recommend you always consult your dentist before you use anything like that.
Home kits are just commercial junk that hurt more than they could do any good.
Finally,the issue of aesthetics (beauty) in dentistry is a huge topic that could take infinite hours of talk...there is always something new every day...I recommend you visit the ADA website www.ada.org for more info.
I hope i helped...i know i talk too much...;) lol