DICE's Alan "Demize99" Kertz has confirmed that a number of changes are being made to Battlefield 3's post revive system, which differs from previous Battlefield games. Kertz provided specifics for how the system works via his Twitter account.
After a player is tagged for revival, they will only have access to a pistol and will remain prone until they accept the revive. They will remain in low health until doing so. The pistol allows them to cover their teammate while being revived. If the player declines to be revived, then they'll simply bleed out with their pistol in hand. If you're killed while in the post revive state, it won't count towards your kill/death ratio.
Additionally, freshly revived players will not be protected by any sort of temporary shield, and can be killed as normal.
The new system is designed to prevent point-hungry medics from reviving teammates within a pitched battle only to have them instantly killed by enemy fire. It will allow dead players to opt out of being revived (while offering them a small means of defense) and respawn back at the base without too much hassle. Forced revival is, after all, one of the more annoying elements of the Battlefield games, especially on public servers.
Anyone who's played in the Alpha will have already known this, but it's still good to see that the changes to the system are more or less permanent.