What is Considered a Large Database Table?

[eluser]Fielder[/eluser]
What would you guys consider to be a LARGE database (in terms of number of records on 1 table)? A number that would begin to impact query performance (standard SELECT, JOIN, ORDER BY, GROUP BY statements)?

Right now I expect my database to be 500,000 records in 1 table within 3 years from now. And likely 2 other tables near the same size.

Oh yea, and I'm using mySQL.

Thanks for the opinions.