First: I apologize to everyone using CACTI for the plural of CACTUS. You're grammatically right, and I'm very wrong. But I just don't like the way the true plural sounds in conversation.
So... I recently bought a pair of Vibram FiveFingers KSOs (all terrain), and being in a nice, hikeable part of Arizona, thought I'd try them out.
Result: Beware of cactus! If you live in a cactusy area and decide to "go barefoot," take extra care. Although the KSOs performed admirably against a few nasty cholla (aka "jumping cactus" according to Tucson natives), they were nonetheless pregnable between the toes, where a mesh fabric provides breathing and stretching room but not toe armor!
Still, it's pretty impressive to stomp on a cactus and come out mostly unscathed. So if you're like me and can't seem to hike without getting impaled a few times, KSOs might not be the best plan for desert (spiny) terrain. Unless you like the adrenaline rush.