I was approached by a client who suggested they wanted to import 1 Million businesses into their Sobi2 Directory. I really think importing 1,000,000 listings into a business directory will hurt your chances of success rather than help you. Not to mention it could potentially slow the speed of your Joomla website to a crawl.
When you have 1,000,000 entries to search in the database, it's going to bog the search and category pages down considerably, not to mention needing a bigger server to handle it. You would need a quality hosting platform, not the $6.00 account from Godaddy, that's for sure.
I recently ran across a client's website that was not allowing visitors to choose the Next and Previous links at the bottom of the page in the Sobi2 Component using the SobiSEF plugin to create the SEF URLs. As it turns out, the client is constantly adding new listings to his directory, and every 20 entries or so causes an additional page number to be created. That's when the trouble started showing up.
Read more: Sobi2 Tutorial - Pagination Next and Previous Links Not Working