I second all previous answers, adding some explicit reasons:
- MySQL issues Warning exception when you try to store string longer that field width - you won't get them in SQLite, so not only you're string will be different between dev and production, but also program behaviour
- bugs in both backends are different - I remember that once I tried SQLite for dev and MySQL for production, but it turned out that I discovered a bug in MySQL backend which was not present in SQLite one. So I filed a ticket for it and switched to MySQL for testing :-)
And you can even try to compete with SQLite in terms of speed, take a look at my answer for other question:
Increase speed for MySQL table creation in Django?
