Win7 Ultimate is really only good if you want all three of these aspects: more than 16GB of memory, joining a domain, and Media Center. If you just have either more than 16GB of memory or need to join a domain, get Pro. If you need Media Center, get Home Premium.
There were initially promises of extras that would only be available with the Ultimate edition, but those never materialized. I know, I got the Ultimate edition specifically for that.
Oh, there was one more thing that was only available on Ultimate and Enterprise: Bitlocker. Worthless. Easy to hack if you have the boot key. The only way it is useful is if the system has a TPM. There's a reason why most companies who use full drive encryption use third party...