It’s certainly possible that the Spyder 3 is worlds better than the Spyder 2 was, but I recently replaced my ailing Spyder 2, and decided to try an Eye-One Display 2 instead. The Spyder software has never worked really well under Snow Leopard, it’s always taken a pretty long time to run. With multiple monitors, that adds up. After I took the Eye-One out of the box, I immediately ran the easy config mode on all of my monitors, and with very little effort, they all look much better! With the Spyder 2, there were noticeable color shifts from monitor to monitor, even calibrated to the same target. With the Eye-One, this is mostly just gone - they’re all finally calibrated closely enough that it’s not distracting moving from one to the other. The software is simple, and it has the nice touch that it runs a location routine beforehand to find where on the monitor the sensor is positioned, so you don’t have to get it in any specific spot.
Overall, I’m very pleased with the multi-monitor calibration so far, without even delving into the advanced features or printer profiling (which also seem to be better than the Spyder 2).