Currently, the OpenMacGrid (OMG!) has over 800 Macs connected. Since many of these Macs have more than two processor cores, this number translates to over 1000 processors, with a total computational power of over 2.0 Tera Hz (a Tera Hz is 1000 GHz!). At any given time, only a subset of these 800 agents are available for work. Looking at the widget on my machine it looks like about a third are available at any time and often there is spare capacity.
So if you have an idea for a project now looks like a good time to submit it.