There are different versions of the ws2801 chip; some for 5v and some for 12v.
Daniel Garcia made a good library to use SPI EXTREMELY efficiently to drive most led strands (in the megahertz)...at the cost of some chip functionality because of how low level the code is.
http://code.google.com/p/fastSPI
Also
LadyAda made a great library for SPI/and bitbang control of ws2801 - it's not nearly as efficient but it easily outputs hundreds of frames per second on a 64 rgb strand.