Not enough options; it has come up maybe once in my FR campaign (where the phrase "DMZ" takes on a WHOLE new meaning), and maybe once in a friend's campaign last year. So it's closer to about 3% of my total gaming sessions in a year?
Anti-magic is a constant in my version of Darksun. Whenever powerful magics and psionics are unleashed against each other something tends to happen. Also, the NEN used and created by the ancient 1/2lings automatically cuts off the collecting of energy for magic. Meaning- you use what is memorized only in a "normal" game world.
The use of anti-magic or anti-psionic zones can be a crutch but I use it to give flavor to the story and to make Players think a bit before rushing into a situation.
I voted 25%, but probably it is about 1/6 of the time. It's a 16th-level party these days, and rogue has a ring with three more charges of anti-magic in it. The party uses it mainly defensively. When we went through oh, Deep Horizons I think it was called, the official WOTC module by Skip WilliamsI believe, there were beholders in there that almost toasted the party (level 13/14 around that time) with their coordinated anti-magic cones and desmodu/troll fighter servants.