Someone in their eternal wisdom added NO_ENGINE_SUBSTITUTION to the TRADITIONAL SQL mode in MySQL 5.5. I can't fathom how a totally mysql specific behaviour one way or another is more traditional than the other but this makes it impossible to use MyISAM with MySQL 5.5 (it's a pita anyways as you need to add default-storage-engine=myisam to your my.cnf as I learned from a mysql bug report...). I have timed drush si -y minimal to be about 6.5s with InnoDB (per file, on tmpfs) and 2.8s with MyISAM(on tmpfs too). Knowing the hundreds of Drupal installs created while running tests this is no triffle matter for developers. It does not affect any users in any ways, what so ever it only cuts the time needed for tests in half on MySQL 5.5. I have copied the meaning of TRADITIONAL http://dev.mysql.com/doc/refman/5.1/en/server-sql-mode.html#sqlmode_trad... from here into the patch. It's the same in 5.0 and 5.5 -- just 5.5 also has this accursed mode.