You can take 20 on perception tests when looking for traps.
The rules say it, so do the devs.
It's even a specific example of taking 20.
The only negative repercussion to failing a perception test is that you don't see it. Not seeing something may have secondary negative effects, like that unlit train running you over, but it's not a result of the skill check failure.
It's not metagaming unless the players are using knowledge the characters can't reasonably have. "I'm checking the area 10' west of the east door, and 5' south. Ok, I found the only trap in the room, let's go."
It's perfectly reasonable for someone to check for traps on that gilded chest, or on the door to the high priests sanctum. That's not metagaming, that's being reasonably cautious. Going over it multiple times is probably a good idea, those trap makers are devious. As to checking every single 5' square you're going to travel through, that's just nuts. Still not metagaming, but taking 3 days to go down the hall is insane and totally paranoid. Unless you're in the legendary hall of a thousand traps, bane of adventurers and nightmare of rogues. In that case, paranoia may be your only chance at survival.
It's been my experience that groups having to put up with rogues that check every freaking square, soon get sick of it and either kill the rogue, talk them out of it, or leave them behind. It's kind of like a mage checking everything he sees with detect magic, rather than just the pile of loot you just got, or the suspicious painting that seem to be watching you.
Freds pretty sure this chest is trapped, and he doesn't want to take any chances, so he takes 20. He looks it over good, and doesn't see anything. Not good enough, maybe he missed something... so he goes over it again, this time peering into the cracks with a light on the off chance of spotting something. Still nothing, not giving up. He thinks back to what his mentor taught him for a bit, then starts looking for any discontinuity in the wood grain and metal. Nothing. There's no way the noble would leave his magic seal in an untrapped chest, would he? No, but Fred still can't figure it out. Hmmm... Taking yet another look, trying to figure out what traps could be there, Fred finally notices something he hadn't before. The lock is obviously a Smargaff design. Those things are tough to open, but they also have 3 inch bolt sticking up on the inside, and the placement of the lock wouldn't give room for that bolt... Ah Hah! This lock must be a decoy! Carefully peering inside the keyhole while carefully reflecting some light in it, he see's it's not deep enough for the normal key a Smargaff would use. It's definitely some kind of trap meant to fool people trying to pick the lock. (DC 30, take 20 + 11 skill = 31, a success and couple minutes)
Fred then searches it for the real opening mechanism and finds it, a set of brass buttons that must be pushed, and in trying to open it, triggers the second trap (DC 34) that his previous search (taking 20 for a 31 total) missed. Guess his GM really wanted to make things difficult.