Apparently, while the console won't be always-on, games will have to be installed on the HDD, and they will be bound to Live accounts. Once installed you won't need the disc anymore to play the game, but if you give the disc to someone else it will cost a "pre-owned" fee. We still do not know the price.
"Microsoft did say that if a disc was used with a second account, that owner would be given the option to pay a fee and install the game from the disc, which would then mean that the new account would also own the game and could play it without the disc."
Soooo... about that...
UPDATE: According to Xbox Support this information is incorrect, but other sources still say it is true, so who knows?