arcane lab

[Juggernaut GO]

came up on sunday with arcane lab.  If I play arcane lab and have already played 2 spells during the turn, can I no longer play any spells since I have already met the quota of arcane lab, or does it not check past game state when coming into play?  

Also, does arcane lab count as the one spell per turn once you play it.  I am under the assumption that once it is in play, the stack is clear, arcane lab has already resolved and then you can play 1 more spell that turn.

[Toad]

The Arcane Laboratory will look back in time to see if spells have been cast previously. It will also see itself being played.

Basically, Arcane Laboratory counts towards your 1 spell limit.