On the 2K boards, one community member found that when his brother attempted to play Bioshock on another account (on the same PC), the software prompted him for a serial number. He asked (ok, whined a bit) as to whether or not this serial would count toward another of his 5 activations. This was 2K's response:
2k Tech JT writes: The other way to view this, is one USER has purchased the game. Not the whole family. So why should your brother play for free?
Because remember, your brother still wets the bed. And sharing no longer exists in the digital age.
Especially with bed wetters.
Update: 2K has contacted us to let us know that 2K Tech JT is in fact not an employee of 2K, but rather an outside contractor who is now, it seems, being investigated by the company.
Please note that the forum moderator has been incorrectly quoted as a 2K employee. The individual, "JT Tech 2K" works for an outside tech support group and is not an employee of 2K. Additionally, 2K is investigating the validity of the post.