the way ARB designed the top unit it now has molded ridges to help guide the rain out. It explains it on their site. I honestly don't see where the moisture would become a problem, every jeep brings moisture into the intake, but it's vaporized before it gets to the engine. you'd be amazed at steam's cleaning ability in the engine.
plus, have you ever heard of "water injection"? It's where a small sprayer of water is added to the intake, to keep the engine air temperatures lower. it's sprayed as a fine mist, which cools the air. it's been used for probably the last 20 years with positive effects, and it's even been outlawed in various racing circuits due to the unfair advantage it offers in engine performance. ever notice how your jeep runs better in the cold weather than the heat? from a performance standpoint, a snorkel does bring in cooler air, which is a plus.
but if you're looking at it from the true offroad perspective, it becomes another part hanging off your jeep. i've seen them ripped off, crushed, and even broken in half. you'll have to work harder to try and avoid damage to it. as far as water fording, if you're going in water deeper than your factory airbox, i'd say you have bigger problems.
