Note before reading: All this is based on MY experiences with the "Wonderous" (I'm Joking and using this word lightly) Paper clip. If you can pick something that I cannot with these cheap metal "thingies," I will feel very happy to hear about them.
The reason I care about paper clips at all is that I watch MacGyver. Whenever he "Picks" a lock, I get a little upset. Such a CHEATER.
Oh, well.
As Stlbolt said, It really depends on the lock...
And almost never with just a paper clip alone.
Are we talking Sledge? I say never.
Masterlock? I believe even these lowly locks cannot be defeated with a paperclip.
What about the lock on the file cabinet in my living room that came from the Marc's store down the street? Yeah...Piece of cake, but do not forget your tension wrench.
I dislike the paperclip greatly, for it always gets me very angry

.
I have given up on them, and just use SouthOrd. I suggest the same, but testing the boundries of our weak, paper-holding friends is rather tempting... Every so often, I do admit to using them, but with VERY little sucess.
But it can be done.
, -._,-. BEWARE, I am weird.
\/)"(\/
(_o_) The only way to make something foolproof is to keep it away from fools.