It appears that disk IO and throughput are back to the speeds of Snow Leopard. On my three MacBook Pro machines, two with 160GB HDDs get 40MB/s to 55MB/s, my other with 5000GB has gone from 50MB/s to 70MB/s. My Firewire drives now read/write at 75MB/s, up from 40MB/s. This was major complaint when Lion was released, most people noticed a slow down in boot speed, IO has improved and the machine doesn't grind to a total halt when paging out. I have also noticed that external HDDs now spin down when you eject them. No need to go in to Disk Utility to eject the whole drive (not the partition) from there to get the disk to spin down and park the head. No more unplug and pray your data didn't get corrupted.