Q: When the rat tokens summoned by the "Lab Rats" sorcery are slain, do they count as creatures in their owners graveyard for purposes of spells affected by this? (e.g., "Soulshriek", where "Target creature you control gets +*/+0 until end of turn, where * is equal to the number of creatures in your graveyard").

A: Cards that count creatures in the graveyard only count cards in the graveyard. Token creatures are counted as going to the graveyard for effects that trigger off going to the graveyard but dissappear as soon as they hit the graveyard.