Squential turbos are great for helping to elimiate turbo lag, as one turbo usually operates in the 2k-3.5k rpm range, where the other turbo kicks in above 3.5k. If you're looking to make usuable street power, it's something you might want to look into. If you want big power, go with a single turbo properly sized to your engine configuration. Read "Maximum Boost" by Corky Bell. It's the best forced induction book out there.
__________________ "If a man hasn't found something worth dying for, he isn't fit to live." - Martin Luther King Jr. | 
sequential turbos. good idea? 
