I love my iPad, use it heavily every day. I knew it was a "first step" when I bought it, and knew the next version would have cameras, much faster graphics/processor, etc.
I will definitely upgrade on Friday. I already sold my 64gb 3G iPad to a company online. It will have cost me $270 to use the original iPad for almost a year as they paid $530 with free shipping. That's cheap rent for something that's been so useful.
Unfortunately, I can already see the first iPad's usefulness being phased out. The iPad 2 hasn't even been delivered yet and Apple has apps that only run on it. The iMovie app only runs on the ipad2 and iPhone, not the ipad1. The capabilities of faster processing, much faster graphics, more RAM, 2 cameras and a gyroscope will allow developers to make very cool apps that won't be compatible with iPad1. Planned obsolescence will be faster than usual I fear.