Panda is fully integrated into Google search and it is a particularly nasty filter to have applied to your website. Furthermore there is indication that Panda and Penguin combine to produce and “Uber Penalty” effect. Some say this means a double flag spells the death of all trust.
Because of how serious the penalties are it is pertinent to optimize every portion of your website that can have an affect. The video above shows one way Google may use your page speed against you.
See more on YouTube.