Are there any consequences to picking locks? I know there are if you, say, pick the lock off a chest in front of someone at The Friendly Arm, but what if that person weren't there? Do you still get penalized in some way if no one is around to see you do it? Whether it be a chest, door, etc?

If nobody sees you, or hears you -- silence is a factor -- then there are no consequences. But be aware that some containers can contain scripts that summon 'super psychic' guards. You have been warned. :-)

Dangit

Well, what if I don't see the super-psychic guards when I'm done? Will they still come after me? I'm trying to play my character as straight an arrow as possible...but there's nothing that says Imoen can't do anything...:-p

So long as you get out before they see you (or rather talk to you) then you get away with it.
One way is to loot the chest and then hide in shadows / invisible-potion/spell before the guards appear.

You will first see a message that somebody has noticed you. That is the cue to take an invisibility potion, or leave the area immediately. So long as the guards don't get the chance to initiate the "I SERVE THE FLAMING FIST" dialogue, they won't turn hostile. And even if they do turn hostile, you can leave the area (through a transition door, go upstairs/downstairs etc.) and they won't follow you, neither will the entire Flaming Fist be on your tail. There will be a consequence of them turning hostile, though: you only get the option to bribe them, or fight them, and you lose reputation (-1 point) for that -- kill them, and it plummets (-5 points).

Edit: Oh, and it doesn't matter which member of your party commits the deed, or gets caught: you're all in it together.

I'll just add that if you're using the BG2 engine (BG2, BGT, or Tutu), hostile guards WILL follow you though transitions, so you're much better off just avoiding conversation and never entering that buliding/floor again.

Edit: Other hostile creatures will pull the same stunt as well, of course.

One thing I would like to mention. You are talking about lockpicking and not stealing. If I am not mistaken, you can lock picks without any consequences as guards are only summoned when you actually open the container. Lockpicking gives some experience points so it might be good to lock picks even if someone is around and you don't intend to steal the stuff. :-)

You can pick locks without repercussion. Opening the container with witnesses or the "summon" script is another matter. And to clarify Vitek's comment, BG2/BGT/Tutu give XP for lock picking, vanilla BG1 does not.

Oh, sorry. I don't even remember when I played BG 1 in it's original engine for the last time, so I wasn't aware it doesn't work this way there.

another thing, you can go to people's houses at night, at least some people will go to sleep and not mind you looting all their valuables. I haven't actually done research on how many people do leave their doors open and go to sleep at night, but I accidentally went through a house, lock picking all the containers and taking all the stuff, before realized there was a person sleeping there, but there were no consequences I know of.

A lame trick you can do is using the charm spell (or Algernon's cloak). You charm the owner and move him/her away => nobody sees you => PROFIT!
You charm the guard who was going to kick your arse => he loves you now => PROFIT!
You can be very very lame with that cloak, but I shall leave to you figuring out how to steal lots of stuff with it without losing reputation :D (also do not abuse it, because it can be seen as cheating and might bore you. Unless you are a chaotic neutral thief of course! :D). Unless you have BGT installed. Be warned.

Or you're using Tutu/Easy Tutu. It's a quirk of the BG2 engine...

Well, Tutu and BGT are pretty much the same. I do not know the exact differences, but as in Thermodynamics, the process does not matter, but the result!

Actuall, no they're not. The only constant between them is that they both use the BG2 IE engine. Other than that, they are both totally different, with totally different roles.

Fixpack mod.