I run a MacBookPro6,2. Purchased December 2010. 2.8 GHz dual core i7 processor (got it about 3 weeks before the quad cores came out). Configured it with 500 GB 7200 rpm disk, largest available at the time.
Rendering video is probably the most strenuous thing I do as far as this machine goes. Final Cut Pro 7. I recently did the MacSales swap out for a second internal drive in place of the optical disk. 1TB 5400 rpm for the second drive. My rendering times have been greatly reduced, but I still wait for a long time. I also have a 1TB iomega external hard disk connected via FireWire 800. It seems that the second disk is what improves the rendering times the most, whether it is the internal or external. Cheapest solution is the external, then you don't need an external optical drive and you don't void the warranty if it is still under warranty.