Disclaimer: I'm a developer on the SQL Server team at MS. You can get a lot more out of SQL Server and MySQL if you tailor your design to take advantage of the features that each has to offer. Properly tuning your database can help you avoid having to throw more hardware at the problem. I'm not sure what the best books are for MySQL, but for SQL Server be sure to check out the "Inside SQL Server 200?" series (there are editions for 2005 and 2008). If you read and understand those 5 books you will understand the best practices for designing SQL Server databases.