Firstly a little bit of information about spawn protection. Your protection lasts two seconds from when you spawn and is cancelled by anything except aiming with your mouse. This means you lose protection if you shoot, move, change weapons, drop gadgets, revive.. and so on. You receive protection when spawning on team mates, spawning on flags or spawning in your deployment zone – the latter not being important unless you are being base raped by air.
In vanilla and Back to Karkand maps spawn protection was not a massive problem. Fire tended to come from a longer distance and with the black pop in screen it took too long to locate, aim and kill the player shooting at your team mate, especially earlier in the game when protection was only one second and was cancelled by moving your mouse.
However after the change to two seconds, allowing aiming and very short black screen in CQ maps, spawn protection has become a game mechanic that can be used for offence, which is good in a game that promotes defence more than most. In conjunction with enemy players being in your face much more often in close quarters, utilising spawn protection leads to multiple kills off spawn regularly.
Simply spawn on squad members you know are underfire and do not move. Line up your shot and get ready. If the enemy targets you and unloads wait longer until they reload. If they don’t simply kill them. This may sound like a lot to do in 1 1/2 seconds but really all you need to do is locate the player and aim at them. You can skip waiting for them to reload and just open fire if you like.
The blackscreen seems a lot quicker on the new maps. Maybe everything is cached, Dice mentioned that they cannot remove the blackscreen on spawn entierly because they preload textures/meshes while it is there. Basically it prevents you seeing massive pop-in on spawn.
Spawn protection is even more fun to abuse in the larger player limit servers for close quarters. Go nuts with it, I know I will.