Vadim Tkachenko posted an interesting benchmark of MyISAM vs InnoDB vs Falcon datatypes. (Falcon is the new backend that MySQL started developing after Oracle bought InnoDB.) For me the interesting part is not the part with the alpha code -- Falcon is competitive for some queries but gets absolutely crushed on others -- but how InnoDB is around 30% faster than MyISAM. And these are pure selects, supposedly where MyISAM is best.
Of course this is a small benchmark and YMMV, but this is encouraging to me because it suggests that if I ever have to use MySQL, I can use a backend with transactions, real foreign key support, etc., without sucking too badly performance-wise.
(It also suggests that people who responded to the post on postgresql crushing mysql in a different benchmark by saying, "well, if they wanted speed they should have used MyISAM," might want to reconsider their advice.)