Re: Explain this about the random number generators
 

[ QUOTE ]
The downside to shuffling the deck once and keeping it for the hand is that it encourages hacking. As far as I can tell there is very little extra computation required to get a new shuffle for each card, so the sites should go with the slightly better alternative. If nothing else it soothes the nerves of paranoids.

[/ QUOTE ]

Actually, not running the PRNG for cards that are never dealt saves CPU load. PRNGs are semi-expensive.

As you said, generating the whole shuffle at once is a security issue, potentially, because PRNGs always generate the exact same sequence of numbers (cards) given the same starting state. If there's a problem with entropy collection or some other issue that allows someone to know the starting state, then the entire deck can be accurately predicted. If, on the other hand, the PRNG output stream is sampled at unpredictable times, how do you predict the next card?