Brandon,
One of the things I really like about fixtures is (as DHH said) you can revert back down to whatever version you like, make a change to the migration (for example, add a field you didn't know you needed), then revert back up to the current version. Then, I use fixtures to load all my sample data into my DEV DB and I am back in business...about 20 seconds from start to finish. I can't speak to how/if you can do that with SQL scripts, but I know it's a nice feature of migrations. It's also all done independent of the particular database, which is nice when you work with more than one (MySQL/PostgreSQL/etc.)
Nathan
