Basically, considering that Ultimate is for power users who use their computers as a home office, would I really need Ultimate? I'm considering that Home Premium may be lighter on my computer. I use my P.C for:

Internet (Mozilla Firefox)
Homework
Word Processing
Kuju Rail Simulator
Ship Simulator 2008
Microsoft Train Simulator
Microsoft Flight Simulator X (eventually)
Microsoft Train Simulator 2 (when it's released)
Graphics work (Corel Paint Shop Pro)
Animation and Film Creation (Macromedia Flash and Windows Movie Maker)
Music (Windows Media Player)
Chatting (Windows Live Messenger)

[Krlll]

Attributable to DuckieHo from OCN

Premium vs Ultimate
Ultimate includes additional features which are not available in Premium. The choice is up to the user if they require all the additional features.
*WinSAT: scans system to determine bottlenecks and sets optimal settings for gaming
*Ultimate Extras: bonus apps that Microsoft will release exclusively to Ultimate. There are currently two with more planned: Dream Scene (motion/video desktop background) and Hold'Em (Texas Hold'Em poker)
*Multi-Language Packs: Converts the text in the OS to different languages
*BitLocker Drive Encryption: hard drive encryption
*Secure Online Key Backup: allows you to upload your key to a MS server
*128GB Memory support (Premium can only support 16GB)
*Support for two physical processors (do not confuse with multi-core)
*System Image Backup and Recovery
*Full Remote Desktop with incoming requests
*Peer-to-Peer app to connect with other Ultimate/Business/Enterprise users
*UNIX application support: allows Unix environment to run on Windows
*Virtual PC Express
*Slightly more UAC control

Honestly, most users will really benefit from incremental Backup and Recovery feature. While Premium has a similar feature, the Ultimate version is saves file revisions as well as the entire file.