When I first heard about magnetic nail polish, I couldn't imagine it working let alone looking good. I saw it in person recently though and had to give it a try. Several brands already offer the magnetic polish in a variety of styles. I'm a fan of Sally Hansen products, and I had a coupon so I tried theirs.
Use a good base coat. Apply a thin coat of the magnetic polish and let that dry. Working one nail at a time, apply a thick coat of polish and immediately hold the provided magnet over the wet polish, getting it as close as you can without touching the nail and keeping it in place for 15 seconds.
I didn't have a problem with this, but I've talked to several people who didn't quite understand how to do it or found it difficult. Most polishes instruct you to use the magnet for 10 seconds. I think the effect was much better if you do 15 seconds. If you're nervous about holding the magnet too close to your nail, hold it a little further away and add a few more seconds to the time. Also, shake the polish frequently because the magnets fall to the bottom. The polish itself was easy to apply, but do keep the top on it while you're using the magnet (it detaches from the top) because this stuff seems like it will get thick and goopy quickly.
It looked really cool, and I got a ton of compliments on my nails. My mom tried it too, and while really liked it, she was frustrated that all of the nails didn't look uniform. If you are seeking perfect nail art, look elsewhere. There is a randomness to how the magnets will look on each nail. None of our nails looked all that different from the others, but they weren't identical either. I liked that, but it was hard for my mom to get used to.
This polish chips a little more easily than many of the other Sally Hansen polishes I've tried, but it will last a few days chip free. I recommend the Dries Instantly top coat Jael reviewed a while ago. I applied the top coat every second or third day to make them last a little past a week. A good base coat and top coat go a long way here.
Overall, I thought it was a fun little gimmick: one part nail art mixed with one part science experiment. Even if you aren't great at doing your own nails, this nail art is fairly user-friendly. Now that so many brands are making it, it's also fairly affordable. Sally's version costs around $7.99 (in stores, online it cost $9.99 plus shipping), and Sally Hansen Coupons are abundant (most of the magnetic polish displays I've seen have a stack of $1 off coupons attached). I liked the look and easy of application enough that I might even buy another color.