I used the silica pearls for a few months before I switched. The benefits are that you really only need to change it every 2-3 weeks (per cat) and that it is very light-weight and easy to sort through when scooping the solid waste. However, it is very expensive (for litter) -- a 3-week supply costs about $18 Cdn -- and my main concern was the dust. They market it as dust-free, but in certain light I could see clouds of fine particulate suspended in the air, and after using the litter box the cat would be coated with dust. My concern was that he would then ingest the dust during grooming. The other problem is that because it is round and light-weight, it tracks a LOT. I was forever chasing little white pearls with the broom. They came out with a low-tracking variety but it wasn't much better.

Now I use "Yesterday's News" recycled newspaper pellets. It is cheap ($10 - $15 Cdn for a huge bag), biodegradable, and it actually smells better than the silica. (It seems to have its own odor that counteracts the litter smell quite well). Only downside is that it's heavy and one goes through a lot, so storage is an issue. Also, more finnicky cats might reject it because the texture is so different.