Practices to keep SQL Server databases easy to port to MySQL? We've developing an ASP.NET Web application that is to be designed for MS SQL Server 2008. I'd like to minimize my future dB admin's headaches should there be a need to migrating over to MySQL.

With that goal, are there any specific design patterns or features we should avoid on MS SQL? Issues that trip over the MS SQL -> MySQL migration tools?
Yeah, plan on using none of the SQL Server features like Geography data types, SQL CLR, filtered indexes, top, CTEs, etc.

I'd say don't bother trying to program for multiple database platforms.  Pick a platform and that'll be the platform which the app runs on.  If the app needs to be moved to another platform later deal with it then.  Otherwise you'll spend so much time trying to figure out if the code can be ported to both platforms that you'll get no where.

If you are going to plan for a MySQL migration, why not also plan for Oracle, Sybase, NoSQL, Progress, etc?