I'm with Dena, I use Petromalt or Femalt too. I only have to use it rarely. When I hear or see one of them starting to cough I give them about an inch from the tube on my finger and they lick it off happily. They like the taste and would lick it right from the tube.
I know that people have reported a lot of success with the hairball remedy foods, again, like Dena said. The hairball remedy foods are higher in fiber, which helps the ingested hair pass through the GI tract easier. You can increase the fiber in the diet yourself by adding a tablespoon of canned pumpkin (not pie filling) to the food once a week, or more often if you are noticing a problem with hairballs developing. Canned pumpkin can actually be given daily if you wanted. Just back off the amount if you notice loose stools. It's a great source of fiber as well as nutrients.
They also sell various treats made for hairball relief.
My mom swears by butter! I know it sounds nuts - but she has a long hair cat and every morning Miss Kitty goes running to the kitchen for her lick of butter! My mom gives her a bit every morning - it's her special treat and she loves it and licks it right from her finger. According to my parents (who pamper and adore this cat!), she has never had hairballs.
Brushing daily, and occasional bathing - if you can get the cat used to it which can be a scary prospect to say the least, will also help keep the amount of ingested hair to a minimum.
The only negative effect from mineral oil in animals or people could be diarrhea. It's totally safe to use.