[PhasmaFelis]

I would rather spend 8 hours at home giving the interviewer a realistic impression of my abilities than 1 hour mumbling over a whiteboard and getting trashcanned because the interviewer mistakenly thinks that whiteboard skills prove anything at all.

As for receiving outside help, if you're judging applicants solely on their homework results, you are Doing It Wrong. The best interview I've ever had gave me a take-home programming assignment by email, then when I came in the lead programmer asked me to explain the program line-by-line and justify various decisions I made. I got the job.