I've got a 5m led digital strip,WS2801IC 32pcs IC+32pcs 5050 SMD RGB/meter with a total of 160 (32*5) LEDs. I've paired this up with a duemillanove and a 5V 5A PS. On the arduino, it's wired off of the ICSP header to Clock and Data pins on the strip and then pulled up by 5k resistors similarly to this. I've ran the fastSPI test leds PDE and the adafruit WS2801 strand test PDE, with consistent errors after exceeding about 60 LEDs. The failure that occurs are the first led pixel being off color and some leds toward the end of the string or all leds begin to behave erratically. If I set it to 50 pixels or less, it works flawlessly.