Re: If you're thinking buying mining hardware, read this first
I work a desk job. If I bought the best video card that fit in the thing (it's a decent system, I design tools with Autocad Inventor 3D modeling software) then mined all night while I wasn't there, no power costs. THEN, surely it is very profitable... 
Except that you'd be stealing the electricity from your employer, not to mention that they would have claim to the bitcoins for providing the system, even if you provided the video card, assuming that your employer / network admin is ok with you making hardware changes.
If none of those things bother you and you're confident of getting away with doing it, then easy profit for you!