We gathered together our ideas of MySQL improvements on this page http://www.percona.com/percona-lab/dev-plan.html
and we are going to implement some of them.
My favorite one is – make InnoDB files .ibd (one created with –innodb-file-per-table=1) movable from one server to another, however it is sort of challenging.
Probably next one patch we want to integrate is Google’s smp-fix or Yasufumi’s rw-locks (we are going to test both before)
On this page http://www.percona.com/percona-lab.html you can find links to our current binaries and patches.