The Falcon storage engine
Falcon is a new MySQL backend that's just been open sourced. Here's an interesting video presentation from the June 2006 Boston MySQL meetup on Falcon's architecture by the principal author, Jim Starkey, who invented MVCC.
My takeaway is that Jim is trying to combine in-memory approaches with traditional disk based ones, and best support the load of modern web applications with the capabilities of modern hardware (SMP+64bit RAM).
Here's a page with a Falcon talk synopsis too if you don't have time for the video.
Jim alludes to a lot of change that he'd like to pull of once the base engine is released :
moving to google-like simplified searching for when you don't know where what you want is located (db-structure agnosticism),
removing varchar size limitations,
security tuned for extranets and connection-pooling appservers, where every real-world user is the same db user, so db security isn't worth all that much.
Update:Sitespect's Eric Hansen points me to the enlightening
Falcon Storage Engine Design Review
and on the same blog I found some interesting benchmarking of falcon vs innodb vs myisam.