After reading the article about intake systems (issue 59, p130), I've been kicking around the idea of going back to the stock airbox, too (with an AFE PG-7 drop in filter). They showed that there really isn't much hp difference between sucking hot air through a big filter or pulling cooler air through a smaller filter. In fact, the stock airbox WITH the stock side cowl duct and a drop-in PG-7 filter made a couple more hp than the stock box with the duct removed or the big conical AFE PG-7 alone. And that was on a ~400hp '99.
I'm not all that interested in picking up another 5hp or so, but to get the air filter out of the elements (it's been dusted pretty good with snow a few times) and maybe pick up a percent or two of milage might be worth the change for me.
Probably my biggest hang up about the change though, is that it would be the third "lifetime" filter I'd have bought for my truck...