I installed a second hard drive into my Alienware M14x by replacing the optical drive with a caddy. I installed lion on the second hard drive, and it boots fine, but it's really slow after it boots. Sometimes when I click on anything, it just hangs for about 10 seconds then loads, but it's pretty inconsistent - sometimes its fine, sometimes it hangs. It's odd because I had lion working perfectly fine in the primary HDD bay, but when I move it to the optical drive caddy, it's slows down.
I was having this same problem in Windows, but I fixed it by installing Intel's Rapid Storage Technology drivers. Is there some sort of equivalent Kext, or something else that I should be doing to make it work properly? System Information says it's got an Intel 6 Series chipset. I know the optical drive port is only SATA 1.5 Gbps, but I don't think that should really affect it as much as it is.