Now that MySQL 5.4 (internally code named performance version or summit) is officially released, I can tell you that I used MySQL 5.4 alpha for my Nehalem scaling studies in my earlier blog - MySQL Scalability on Nehalem systems (Sun Fire X4270). I am waiting to get hold of a 4 socket Nehalem system to see we scale; but that will have to wait for the MySQL conference to get over.
Allan managed to get slightly higher Sysbench Read-Only numbers than mine using the latest MySQL 5.4. Interestingly Solaris does better than Linux. Probably a bug since many of the optimizations in MySQL 5.4 are OS independent. But then a lot can happen in 12 months