I need to see how Magento will perform with 1M SKUs; but I'm struggling to find a large data set of sample data to download - or find a feasible method of generating the feed for import (and the import process itself).

1. Does anyone know where I could download a large dataset of dummy data for import (or a sensible means to generate and import it)?
2. What issues do you forsee with having a catalogue size of 1M+ products?
3. Is there a way to share a single products DB with multiple independent stores (different companies)?