This "new" over the counter medication in fact isn't actually new, the active ingredient that is.
It's practically a prescription medication (Orlistat, brand name: Xenical) that's already been on the market since 1999, turned over-the-counter for public use without a prescription.
OTC medications are always in any manufacturer's best interest. No prescription needed for a relatively powerful drug. So access without doctor's consent, equals more sales if advertising is right.
The OTC version (60mg) is pretty much half the dose of the prescription version (120 mg). You're going to have to take it with meals that is relatively high in fat. If the meal is relatively fat free, it's kind of pointless to take the medication. And obviously as with all medication take it with a full glass of water.
And since it does decrease the absorption of fat (remember it doesn't totally stop the absorption of fat, it just decreases the absorption), your fat soluble vitamins will also be affected, hence supplementation may be necessary. Vitamin A, D, E, K.
The medication, Alli, pretty much stops the enzymes found in your intestinal tract that breaks down fat so the fat (important to your body) can't be absorbed into your body. The medication practically stays in your intestinal tract and works there. And when it's done working, you "poop" it out.
The side effects would be your gastrointestinal symptoms. Think about it, since it's preventing fat from being absorbed, you guessed it, the unabsorbed fat has to go somewhere. You might have to visit the "you-know-what-room" a little bit more frequently during your initial phase of taking the medication.