Yes, when Dell accidently ships you an extra one, and you have to send it back :-!
No kidding, I ordered a brand new fully loaded Dell Dimension 9200, with Core 2 Duo, 4Gb RAM and "one" Dell 3007WFP Display, and they sent me two of them by mistake. Even my paperwork, invoice, packing slip and online account says "1", but I got "2".
So humbly, I phoned them and a rather shocked, but controlled, Customer Service lady politely replied that they would send me some shipping labels so I wouldn't have to pay the freight. I could feel the reaction over the phone, but being the professional she was she couldn't just blurt out "holy crap, you're kidding!".
Oh well. Anyway, here's my new guilt-free setup:
I'm using MaxiVista to control my Dell Inspiron on the left, and Synergy to control the iMac on the right, from my center keyboard and mouse.
Bigger is better ;-)